Your husband is likely feeling guilty that he didnt try harder. And she is using her grief to further enhance that. Why does she not "have anyone". No friends? No SO? No other family? Well that was her doing, and at age 28 she can figure this part out herself.

I get that she is grieving and right now she is giving your husband a lot of attention and requiring a lot of attention, but most of this is on your husband.

Talk to him about how you feel. Talk to him about his defensiveness. Talk to him about you feeling like the outsider.

What did you have conflict with SD over? Yes, it is aweful that she never paid any attention when your husband was sick, and now that she needs someone shes all over him like white on rice, but being that her whole world was her mother and mother is now gone, shes probably panicking.

Talk to your husband. If things get really bad, can you get him into therapy? Sometimes it takes a 3rd party to really hash things out.

I would be sure to go with my DH for the sprinkling of ashes if this was me. And I would insist in staying in a hotel! There is no reason they need to be in the family home! And as for carrying his phone around - I have had to deal with this since day one! I cant stand how he feels the need to never miss a call. Like his and her worlds will end if he has to call her back a bit later! Its my biggest turn-off with my DH!!!

Well - on the one hand, her mother just died. I'm in my 50s and dread the day my mother dies, can't imagine having it happen when I was 28. So I can see how she might need her father's support. You say she "recently" died, how recent? 

On the other hand, he can't keep this up forever. Perhaps he should encourage her to move closer to you so he can be more helpful. 

I get it that she's grieving her mother.  Your DH probably feels like he should do anything possible to help her.

I have a SD with mental issues, too.  I've found that I've had to calmly state some basic things that most people already understand.  Like, don't call before 9 am and don't call after 9 pm (because in her mind, her problems require immediate airing).  Like, I'm uncomfortable with somebody coming to the house unannounced late at night (because she cant sleep and is obsessing over her issues and this was formerly her home and DH is here so she can cry on his shoulder).   Like, if you call and if I take the call, don't babble on and on (because nobody will listen her but as a mother figure, I have to, in her mind).

In a quiet moment, you might have to lay this out for DH.  When I talked to DH, he undetstood and made changes.  Before that, I think he thought he had to put up with it.

I do know what it feels like to be the "other woman" to SD. Fortunately, my DH and I were able to work it out and he was willing to make changes.

One thing you can do is establish your own boundaries based on what you need. You're not telling your DH that he can't have a relationship with his daughter, but it can't be at the expense of the relationship with his wife. So figure out what YOU need for health and sanity.

So if she calls late at night, could you live with your DH taking her call, but in another room? Or no calls at all after bedtime or a certain hour?  And, will he agree to turn off his phone or leave it at home when the two of you are out together or having couples' time at home? And couples' time can be everything from doing a monthly budget to doing something, uhm, more fun.

Then disengage as you can. I do understand the irritation of her calls and requests, but you have to think rationally about what affects you and what doesn't. If it doesn't affect you, you can learn to let the irritation go, at least to a tolerable point. Don't bring her up in conversation, and if he does, then nod and uhm hum at him and change the subject.

I have had a similar issue with DH taking calls from his adult kids. No amount of my tears and anger changed his behavior until I started to change MINE. Call during dinner at home? Ok, I pick up my plate (not his) and clean up the kitchen. "Oh, I thought you were finished since you left the table. But you can heat up your plate or please clean it up." Call when we're out at a restaurant? I excuse myself, then get in the car and go home. I am not kidding you, I did that. To this day I don't know how DH got home as we never talked about it. And it's never happened again.

She needs help but your husband is not equipped to help her.  She needs therapy.  I lost my dad 20 years ago and I took it very badly.  I had massive panic attacks.  I had my husband to help but I also ended up in therapy, which helped a lot.  He wasn't equipped to help on his own.  It took therapy, along with his support and some support from my mom.  I ended up back in therapy when I came off the antidepressant and needed him, Mom, my grandma, aunts, uncles, etc.  She sounds about as bad off mentally as I was.  One person can't be there for her especially far away.  He needs to push her to get into therapy.  Maybe she could join a grief support group and make some friends that way.  

I second grief group. Perhaps her father could research some grief groups in the area she lives and present them to her. I think she could get more benefit from a group than talking to her father into the night. 

Your SD definitely has a problem, but YOUR problem is your DH. Is he willing to do anything at all? Is he willing to even hear what it is you need from him? Or is he just spinning, hoping things will magically fix themselves?

Suggest you find a time when you are both calm and bring up the topic with him lovingly. If he's willing to engage in a conversation with you about how to move forward, then there is hope. If he just gets mad and frustrated and won't consider your feelings in this, that's a pretty big blow to the relationship.

Would he consider couples counseling to work through this? SD isn't going away, and things can't go on like this forever unless he's willing to risk his marriage to you. Something just has to change.

and feel for you. You can count on us for support. However, it seems you and your H are stuck - unable to work through this on your own. You both need some insight and new tools to become a team again.

Mental health issues are scary; they're also above the paygrade of most of us. You both need guidance from a professional, so couples counseling is needed. Your DH should also get individual counseling. He's struggling with a lot: loss of his ex; fear and guilt with his daughter; and frustration and resentment in his current marriage. He sounds overwhelmed by issues he's ill-equipped to handle, and is letting First Family dysfunction damage his current relationship, which is terribly unfair to you.

As Merry says, SD isn't going away, and change IS needed. Please get help from a professional so it can be healthy change.