I am so sorry. Teenage girls can be awful. I have the best Mom in the world, and I remember a period in my early teens where I felt anger towards her for absolutely no reason that I could figure out. I'm sure you already know this, but the pain and stress from the accident is contributing to her irrational behavior.

At this point, I think I would quit trying to appease him and handle her medical issues in the way that is best for you.

Go ahead and have a "good cry" and do whatever else you need to in order to feel better. Hang in there, things will eventually even out again.

I think your compromise for the Easter break is a really good one because it is allowing DD to see her family coming in, but also still being present for what is important in your household. 

For any future appointments, I wouldn't arrange it around what works for your ex-DH and do what works for you and your DD and if he moans about it just say how you have scheduled past appointments around his schedule and location, but he didn't make it to a single one so you are not going out of your way moving forward for him to not show again.

As for your DD and her attitude towards you, like the poster above, my teenage years, my mom and I did not get along pretty much at all sophmore year or junior year. My parents are together, but I preferred my dad over my mom during this time period and felt he was more understanding than my mother. In college, our relationship got a lot better and especially senior year of college. Sounds like your DD is stubborn and strong willed which later in life can be good because you know she can stand up for herself, but at this point in life it is negatively impacting your emotions and mental health. Growing up my mom would tell me "I am your mother and I am not here to be your best friend or even your friend. At some point you will understand and respect this." I HATED when she said this growing up because I was a know it all teen and was like "no shit" in my head. Now, as an adult I totally understand it and that is how we raise SD and how we will raise ours children as well. 

Your relationship WILL get better, but unforunately it won't overnight. Just has a lot to do with teen emotions and hormones. As women, we tend to be way more emotional when someone you are trying to do the right thing for is not appreciative and instead is hurtful, but men usually are less emotional during disagreements with their children. 

I can't help but wonder if she treats you poorly (especially in front of her father because a) he makes it harder on her if she's nice to you and 2) it's easier to be poopie to you because you'll forgive more readily. 

Regardless, it's crappy. {{{hugs}}}

Teen girls are the pits at times.  shoot BEING a teen girl was the pits haha.

I think that sometimes we are crappy to our parents because it's "safe" they will still love us.  They can be going through things with school.. friends.. life.. boys and it becomes the parents who get the brunt of the attitude.

Of course, since your DH is the parent most out of reach to her... in a way she probably feels less secure in being a butthead to him (thought who knows.. maybe she does there too)

But, it's easy for him to set up the scenario where "too bad you will miss that time with your cousins".. but I think a stern.  Well.. you know, I'm making an exception as it is so you can go for passover... if I really wanted to be an ahole I wouldn't even agree to that.  Take what you get and be lucky you are getting that.  

And.. stop twisting yourself around on appts... make them when and where is convenient to you.

I think kids rebel against the parent they sense is strong enough to take it.  Something tells her Disney dad can't handle it.  He is already showing proof of undependability in this urgent medical situation.

So is it possible her father is a bit of a Disney Dad so that's why right now it's easier to want to go be with him, especially now that he lives so much closer?   Or is it that right now in this cycle of her life she is relating more to her dad and feels she needs him more right now?  Either way the teenage girl attitude is rough!  Hang in there you are doing great and someday she will see that you were there for it all and she will appreciate that you have that bond.

I let my oldest go live with her dad. They were scheming behind my back so I called their bluff.  He was just doing it for the money.  She came back and I had to get her healthy again.  It was a lesson in who her dad truly is.  He made all kinds of promises but didn't keep them.  Didn't keep food in the house for her.  It was a travesty.   Not saying we didn't have our arguments but the respect for my role as mother came back when she did.  

As everyone has said teenaged girls can be awful.  

The next time she is being mean when you ex is around, confront her behaviour once he's gone again.  She's fundamentally a good child so even if she gaslights you when you tell her to not treat you badly because it hurts your feelings, it will prick her conscience and may help to stop her being a pain in future.

Tell her the truth, show her what's really going on.