My DS and I are going through something very similar @Watchamocauli (fab name btw) and the best advice I was given is that kids will take their lead from you - if you get spiteful and toxic about the divorce (like my parents did) they will think that's the way to behave, whereas if you appear calm (ish) and sad but not dramatic they will accept that.
Yes it's going to be tough, yes it's going to be sad and there will need to be new ways of being all round - you, DD, XH and his family - but all of those will be better than staying in the awful situation you are in at the moment. Divorce doesn't need to break her, my DS is similarly bright and sensitive, and whilst he has struggled a bit, everyone is now remarking on how much happier and calmer he is day-to-day. And I am happier and calmer, which makes for a much happier home life for both of us, especially as XH and his behaviour are now elsewhere.
Take the high road, rise above the vitriol and present your DD with a calm, matter-of-fact demeanour that will reassure her - you don't need to lie, you can say it's not easy for you and you are sad about it, but be careful and age-appropriate about how much detail you give her; I left my XH because he was abusive, so I have REALLY had to bite my tongue about what I have shared with DS, but he will understand more as he grows up. For now he - and your DD - need as much stability and reassurance as is possible. Lean on your friends and family when you need support, not your DD (I'm not saying you are, I just know how tempting it is...and I spent a lot of my time in therapy talking about how I had to parent my mother when I was a child...)
Get yourself a good family law solicitor and get yourself out of there. There are brighter days ahead I promise.