Your situation reminds me of when SD63 was that age.  First, she moved here because she couldn't get along with BM.  Then, once our honeymoon period wore off, she moved back with BM because we were so mean and she always really wanted to live with BM without the other kids there.  She moved back here after more dissention with BM over BM's bf. Yo-yoing that caused continuous upset.  She was always looking for the more permissive place.  DH and BM were also competing to be the most favored parent and SD used that.

If we had it to do over and if I could make DH understand what was going on, we would have supported BM's disciplinary measures (or she would have supported ours).   Staying in one home and having to feel consequences would have been best for SD.  Hindsight.....

Would your DH consider a parenting class of some sort? He treats SD like she is his equal, not his child. A parent shouldn't be constantly arguing with their child. If the kid does something wrong, there should be a consequence. If the kid wants something and the parent says no, there should be no more arguing and there should be consequences for any more bad behavior.

Does he ever try problem solving with her? Can he figure out how to stop the argueing? She wants to go to another gym and DH is not willing to pay. Is there a way she could do something so she could go to that gym? Could she get a job, or do something around the house and get paid for it?

SIL graduated from HS a year early due to the People's Republic of SpermLand cutting the credits required to graduate in order to save money.  SIL was in the transition class for that change.  She had accrued extra graduation credits due to a P2P program she did the summer after her Sophomore year.  So, with parental approval she could graduate a year early.  If there has ever been a kid who needed as long in HS to mature as possible it is my SIL.

To try to mitigate the risk of her working as a night cashier at whatever barred window convenience store would hire her in their one stoplight small town and her having multiple kids by multiple daddies by the time she was 20 I proposed to DW that she take guardianship of her baby sister, she move in with us in a state far far away from SpermLand, we pay for college for her and to help offset some of the cost of supporting her, educating her, and providing a vehicle for her use SIL could provide after school care for our son (then 12),  do the yard work (after school care and yard service was running us about $500/mo), and do some basic house cleaning.  SIL took us up on our offer, MIL & FIL approved guardianship transferring to my DW and SIL lived with us for a year.  

We were so mean for "forcing" her to attend her university classes, do all of her assigned course work, requiring her to make it college level quality, keeping our yard and doing some basic housekeeping, and mostly because we would not fly her BF out or her home to SpermLand for booty calls, that at the end of her first year of University she ran home, got knocked up by her HS BF, had an OOWL spawn, was accepted and attended the local University about 20miles from their home town taking out nearly $100K in school loans that she has never paid a Cent on, had a second kid OOWL marrying her then BF shortly after their second was born and she got empathy charity from the hospital as a single mom that waived her labor and delivery costs on both of their spawn. Yes, the game playing entitled eternal victim mode failures in life.

The only thing I was wrong about in my forecast of outcome if SIL graduated early and did not take us up on our offer was the multiple baby daddies forecast. Both have the same dad.  The likely reason for that unlikely outcome came to light recently.  SIL called DW a couple of weeks ago to come out as Bi.  Apparently she has had a series of GF side pieces throughout their marriage.  So, not much risk of multiple baby daddies.

After returning to SpermLand and getting into the local University she went down a very long track to the plumbing under the proverbial toilet bowl. First she was denied entry to the school of education after years of claiming to be an education major, ultimately failed even a Gen Studies major and was  kicked out of the university for making no progress toward graduation after nearly a decade.  That and they would not process any more grants or loans for her.  She failed more classes than she passed and never repeated even a  single failed class. Unlike HS where social promotion got her through on the back of a Dx of dyslexia. University required her to actually do the work and pass in order to graduate.  No parental signature was going to save her there.

Her grades for her first year living with us and attending DW's Alma Matter were solid mid 3.xx range.  DW pulled some strings to get her accepted and one of DW's mentors/favorite professors took SIL under his wing. He also would keep DW updated on SILs performance so SIL and I could protect our investment and not tolerate SIL burning out monehy.  Her decent Freshman year GPA earned under out constant hairy eyeball and our collective foot to her ass is what got her into the local University in SpermLand as a transfer student.  She never passed all of her classes in any given semester after she ran back home. to SpermLand.

As SIL and MIL were loading up to pull out for their long drive back to SpermLand after SIL's first year of Uni, my dad said to her that she was making the worst decision she would ever make in her life and she would regret it for the rest of her life.  Had she stayed, she would have graduated with a BS, likely with a decent GPA, and with zero school debt.  But... nope.  As the addage goes, you can lead a horse to water but you can't make it drink.

So, based on our experience with my SIL and similar experience of other STalkers, performance wise, these types are extremely unlikely to ever be viable adults or of any significant quality.

My SIL owes shit tons of $ in school loans.  With penalties, interest, default fees, etc... well into the $6Figures for a degree she never completed.  She is scared shitless that the current administration will likely start collecting via garnished wages. She has worked for nearly every employer within a 2hr commute of their home town and no one will touch her with a 10ft pole job wise.  She is one of those who knows more than the boss and everyone else or quits before she is fired or for another job making 50Cents an hour more, thinks she is spe---cial, has attendance problems that are supposedly not her fault, etc... and gets fired.   Their home has been in foreclosure at least 3 times and was saved each time via something called a Hail Mary recovery with the bank.  She and her STBXDH are pulling the plug on their marriage and SIL is begging for a bed or sofa from family and friends as the house is in her STBX's name due to her crap credit when they bought it.  Just prior to getting married.   She cannot afford to quit her school job as a teacher's aid because that is how they insure their kids for medical.

To top it all off, she has very recently come out as Bi, has been cheating on her DH for years, and their eldest just made it clear to both SIL and her STBFreeXH that she disgusts them and they want nothing to do with her or her series of  side piece GFs.

Lower your expectations so you won't be disappointed.  These types are rarely worth the investment in time, money, and emotion that they consume.  It is all so heartbreaking.

IMHO of course.

Good luck.

I hope yours proves this forecast wrong.

Would your DH consider counseling sessions with SD? Family counseling? They can figure out how to communicte or come to a resolution that might work for everyone. A steady outsider can sometimes help. I hate that this falls on you and stresses you out. I agree that she needs consequences. 

Hopefully he lets her go .. DH needs to understands that if she moves back to BM it's not a permanent move, it can be temporary. Like many step talkers told me. Ultimately this is their child, their issue. School is important and she is still a child...DH should definitely take that cell phone away at night if she continues to miss school. 

Early teen year girls are THE WORST. I know that I was a bit of a b*tch around age 15. (With the exception of my Bio D who was actually a pleasure to be around, for real.)

The hormones and the drive to be independent of your parents but no real ability to do so ... recipe for misery.

I realize she has had the pants spoiled off of her but by age 15 she really should start to have a say in her own destiny and future, including which school she attends. Tell your DH that she needs to be allowed space to grow-up on her own terms. She will probably get better grades if she's at a school that she wants to be in. She is less likely to thrive at a school she doesn't want to be at.

In my experience if she has been spoiled up to this point then it's far too late to start going all consequences or heavy handed discipline on her. She will just hate you. At her age the hormones and emotions will block all her logic and reason. He should have been discipling her when she was age 8-12 and she still liked her parents.

Last but not least, you and your child don't need to have to deal with her negative energy and drama for the next 4 years. You and your husband don't need the stress on your marriage. I say let her go back to her Mom. (Or ship her off to boarding school. Not kidding, boarding schools are a GREAT option and a lot of kids actually love the experience.)