This might be true, but perhaps she should try again, and explain how her behavior has improved (after some real changes), how she has become a more stable and rational person now.Has it occured to you that the reason she doesn't want one is that she tried that before but the doctor would rather believe her conservator?
Trying to avoid the doctor/psychiatrist doesn't seem a good idea to me. Doctors are key people in our society, particularly in her situation, and their fundamental goal and purpose is (or should be) to help, not to deprive people of their own phones. I guess she has the (financial) means to consult many physicians, including excellent ones, who can advise and advocate for her.