I'm not sure she has to notify you. Do you have joint custody or does she have sole custody? If joint, then I would think that medical decisions must be made by both of you. If sole, then probably nothing you can do.
Wow, your divorce must have been horrible for her to be so 'vengeful' after all this time. Well, at least your daughter is almost 18. I hate to say this but you have dealt with this for a long time, maybe it's best to continue the way it is until your daughter turns 18. Another year in hell is a small price to pay in order to be rid of the situation(x-wife). If you try to fight her (or defend yourself) now, I'll bet that she will find other ways to make you miserable after your daughter's 18th.
I envy you, I am just starting out on this journey called 'divorce'. We have 15 more years 'together' since our daughter is only 3.