PR and medical treatment

It is over seven years since my husband and I separated and about 6 years since our divorce. We have one daughter who is 15. Our child residence arrangements have changed a few times over the years - but with shared residency for most of that time ( ex classsed as resident parent). For last 2 years daughter has full time residency with her dad as she decided she no longer wanted to spend her weekends with me. During this time we have had periods when our relationship has broken down, and I feel that parental alienation may play a part in this. My daughter has some health problems and has been referred to specialist hospital 70 miles away. Ex husband states that my daughter doesn''t want me there for her appts, but when I asked my daughter she stated it wasn''t up to her, but up to her dad. I did advise her that was not the case. I am concerned that there will be some reason last minute why he can''t take her ( it is his MO,lol). I have told him that I want to take her to some appts, My ex told me he will tell me what is said ( but sure it will be his interpretation) , and that when she is 16 ( Apr 2016) it will be nothing to do with me anyway. Any advice/information re boundaries of parental responsibility in this kind of situation greatly appreciated