Disengagement means you pull back from what you want and need to.  I would not feel guilty for not shopping for SD anymore.  Let BOTH of them feel the sting of her behaviors towards you and serve up your disengagement on a silver platter.  If they want to benefit from your kindness then they both better recognize their roles in you choosing to back off.  Enjoy the day with your bios.  When she goes , and DH starts in, you can either shut him down OR grey rock him.  That means responding with noises, that's nice and other bland answers.  No responses and no discussion about her problems. You have become utterly incompetent to solve anything for him and her.  Don't crack, you are training them  about your new boundaries.  

Wait, so he thought you would chase him down the driveway to go out to dinner with him and the ILs? And without you, he didn't want to go? LOL.

I would remind him that I'm not getting anything for SD, just because that's how I am, and it would help avoid conflict later.

Good for you for setting boundaries and sticking to them - and doing it FOR you, instead of against him and SD, if that makes sense.

You have absolutely no reason to feel guilty and should set reasonable, healthy boundaries. SD is not your child and other than being kind to her, you owe her nothing.

When SO gets angry because either OSD pouts because I didn't do something with them or for them. I always remind him that:

A. No one told him he couldn't go and do the same exact thing with SDs 

B. No one is stopping him from buying things for SDs. 

So how is this my issue?  They are his kids after all and in case he forgot, they don't like me. 

Well, you know your husband best so either don't remind him, at all, or say something like, "Don't forget, Easter is next weekend." If he will get mad, either way, then I guess it doesn't matter, do what YOU feel like doing.

It will feel better for you as time goes on and your disengaging gets better. It'll be more natural.

I don't remind DH about gifts any more and haven't for a while. I used to, when SDs were younger, but only ONE reminder. Then let it go.

If he gets all upset you didn't do anything, then, when SD is not around, remind him you don't do things for people who don't appreciate it. That's it. No argument back to him. This worked with my DH and me not doing much for Xmas. Now DH himself pulled back this last Xmas for the same reason.... he's not received any appreciation.

Keep on it!

I hope you didn't let him bait you into any argument after he returned to the house. I hope you kept watching your show and enjoying your wine!

You are doing this well. You have caught on on how to keep your dang sanity . Thats a huge step.

Out of courtesy, this time only, you can remind him that you arent buying Easter presents for ingrate SD. After that your DH is on his own. Good luck to him LOL

Its a shame these lil B's make life so difficult. Thanks to the shit parenting. Step life could be much happier and more manageable if our spouses held their kids to the task of being respectful. It really isnt rocket science is it? 

What happened that DH and SD returned to the house so quickly? Did she act up? Spill the T! lol 

Good for you! 

"Hey hunni....Im sorry but I did not get your child a basket. I have decided to protect my sanity... and our marriage.  SO... ill need you to now be in charge of her basket. Once she starts being kind and respectful to me we can revisit this in the future...but right now ...for us to be ok....you're in charge of her.

I may also offer to put baskets together with him to show spousal support but he does hers. I do mine. Maybe it will be fun

All responses 

I say "your probably right"  I mean I don't care and its just not worth arguing over 

I say" sorry you feel that way" I mean I'm putting me first because I'm important.

I say "whatever" I mean I just don't give a darn

I say " I don't know" I mean I don't think this involves me or I just don't care

I say " I know you can figure this out"  I mean I'm not figuring this out.