somehow BM overrides DH on how she needs to come on the weekends meaning she will let SD have her way 90% of the time. 
 

Um no ma'am report her to the lawyer for interfering with custody. 
 

Kids do not get to chose like that until they're around 15or so then they can opt out to their hearts content. 
 

Sounds like they're turning her against him and that's not right. Unless the kid is sick with a communicable disease, BM is obligated to drop that kid off every weekend or she can be held in contempt of court 
 

How can you wanna do things with your step kid knowing they don’t wanna be there?

Simple. Don't. 
 

You do what you can but you cannot force them to do anything (aside from giving you basic respect in your home). Make it a safe inviting space for them for them to open up and that's all you can do. 

" I don’t even wanna take pictures with her anymore like I use to. Is this wrong of me?"

Congratulations! You have finally accepted that you are a person with feelings. Those feelings matter just as much as everyone else's do! Seriously, that sounds like growth to me. I remember your previous blogs and it seemed like taking pictures was a kind of OCD that made you feel relevant, because the other people in your life did not. Of course your feelings aren't wrong.

As far as what to do - does your DH have a legal custody order? Like from a court? If so, SD or BM's feelings have no bearing on where SD is during your DH's CO'd time. She goes to your house when the law says she does. If she doesn't see it as a choice, she will likely come to accept coming to your house. 

1.  A 9yo does not get to refuse visitation. If they do, nail the CP with a contempt motion for failing to surrender the Skid per the CO and for interfering with the NCP's visitation. Every time.

2. A 9yo is far more than old enough to know right from wrong and be held accountable to choosing wrong.  Including when they pull manipulative pouty bullshit during visitation of they don't want to do something or if they do not get to do what they want to do. 

Lather, rinse, repeat.

ASAP.  Take BM for contempt of court   Hearing.  She 9 yo you have many years left.   This is the folk in the road of life. Either fight for SD  or give up.  BM is getting her way, now. You must change that

If there's an official CO, then SD and BM have no choice. SD must spend weekends with her father. A child that age is definitely not old enough to make that decision.

As for the emotional side, I get it. Gradually over the years, it's become more and more obvious that SS12 (nearly 13) prefers to be at his mom's. (They split time 50/50.) Understandable. She and her parents spoil him rotten and let him get away with anything. We're big meanies who confiscate electronics at bedtime, make him keep up with schoolwork and won't let him eat in his room.

BM and DH don't give him a choice and are one the same page as far as custody and trade offs -- for now, anyway.

But I can see how it hurts DH's feelings, because he feels abandoned and like he's gradually losing his child. It makes it harder for me to like SS (already a challenge). DH is basically preparing himself for the day SS gets old enough and completely pulls away.

Sad and frustrating to watch.

Anyway, I sympathize and empathize. Ultimately, though, SD and BM should not have a choice in the matter. But your DH is the one who can do something about it.