I hope this is the right place to post for this. It's got nothing to do with my husband, which I know is my main relationship, but the person it does deal with is "family". I say that with quotations because I don't (can't/won't) consider her family.
Anyway. I've struggled with this person from very early on in my relationship with my husband. We (my husband, her husband (my husband's brother), she and I) had to cohabitate for a while and from the moment I moved in, things got weird. I shouldn't say we had to, but for simplicity sake I'll leave it at that.
I think our issues stem from our husband's issues, as bad as it sounds. They've gotten better, but when I came around they hated each other. I was warned about that ahead of time from other family members, so I knew there were issues. I knew things would be weird from the get go, but I feel that for some reason she's(the object of this post) had something against me from day one. It started with an empty milk carton and dirty dishes and has just gone downhill from there.
We had what I've heard considered a "come to Jesus" meeting, which, surprisingly, helped for a while. I've kept my guard up regarding anything to do with her or her husband though, which may be some of our issue.
Recently though, we had a huge blowout. Supposedly I crossed a line by communicating with her husband's ex wife about their kids, and things just spiraled. I told her the only reason I've been civil with them is because of the kids, and she told me I tore her family apart. We weren't nice to each other and both got defensive.
I know this is one sided, but I did apologize multiple times. Both for upsetting them initially and for coming across as rude during said conversation. Unfortunately after my last apology, the discussion went downhill again, which is when I was told I tore their family apart. When I had finally had enough I told her I was stepping out of the conversation and that I wouldn't let her make those kind of accusations toward me.
Up until yesterday, we hadn't spoken. She sent me a message asking if I would babysit for her next week. I'd be lying if I said I wasn't appalled at the request. I mean, I love my nieces and nephews, and I love spending time with them. But to ask me to do a favor without so much as trying to make amends? That's what I'm struggling with...

Sorry this is a huge rant post, and it's a serious issue for me. I hope it all flows together and makes sense. It's hard to type out every detail.