But don't expect it. After 12 years, I'm completely disengaged from DHs adult kids. It's been 4 years. While I have gotten letters from 2 of them (because of DHs pressuring them), both were filled with deflection and total denial of the real issues. Still...I accepted them and responded (via snail mail also) with the facts of the event, that I was ready to move forward, provided changed behavior was implemented. I did my work in counseling, saw my weak points and self corrected so I expect the same of someone who wants to be back in relation with me. Well, didn't take any time to see neither had changed....almost looks like the two planned the "slight" they delivered a few weeks later. My DH was devastated. I laughed.

If things ever improve between myself and DH's kids....I'm handling them with my special saying of "civil and superficial." Nothing deep. Not doing anything for them; no gifts, nothing that family/close friends do for each other. Kind of like at church (or other large community groups); while we attend services together and see each other weekly, I'm not friends or close with everyone there. I treat them with kindness and respect but that's about it. And that is ALL DHs kids can ever expect from me IF we are ever in contact again.

Restoring broken relationships takes a LOT of work and energy. Lots of sorrow of the wrongs done, empathy for the one hurt, willingness to be transparent, etc. Most of the SK issues I've seen on this board and in my other group are just NOT up to the task. 

EDIT: And yes, be grateful your DH has your back as strongly as he does. Not many of us have that. While my DH has taken stands over the years, nothing strong like your DH that sends a damn clear message to toxic behaving SKs.

Rather than avoiding her and avoiding family events that she will be at, you and DH should go to every one of them and make it clear that she is full of shit, toxic, and to bare her ass in front of the family. Every time.

Run her off rather than you and DH running away.

The toxic are the ones who need to have the message that they will be aggressively attacked, ridiculed, and shredded at any even they show up for.  Even if they apologize they need to have absolute clarity that they are not forgiven even if their apology is accepted and if they so much as think about perpetrating their toxic shit again they will get more of the same.  Tell them that every moment for the rest their toxic miserable lives they will be under the hairy eyeball so they had better never forget it.

Bring the pain, bare her ass, and make damned sure every one in the family knows the facts, that she is a pathetic manipulative liar, and that they all need to know it.  Particularly the part where she informed her dad that he will divorce you or not have a relationship with his grand child.  Every parent and GP in the family would rathe puke on her than look at her after that becomes broadly known.

Have fun!

At least your DH has stood up for you! Mine promised too and then folded to the evil SD's - seems grandkids were too much of a threat for him to risk. However he doesn't have a problem risking our marriage!