Oh my gosh, I have that same sick feeling in my stomach from reading your post, that I used to have when my parents would do this to me and my sister when we were little.
This was the worst part of the divorce.. Having them put us in the middle or in charge of these situations.. I still have nightmares from all of that. Please, please, try to not pull her into this, try not to even let her know when you are pissed at your ex.
You will always be her mother and she will alway love you with all of her heart.
Her father will always be her father and she will always love him with all of her heart.
Do not place her having to defend either of you.
Figure out a way you and the ex can have better communication. When the communication fails, do not lash out, instead TRY (I know it is sooo hard) to leave daughter out of it completely,.,
Answer your phone every time your daughter EVER calls. How lonely , guilty and scared she must feel right now to have disappointed you so much.