it sounds like she went to the same group for her gp and specialists and the group as a whole dropped that insurance.

insurance companies put lists of participating doctors on their websites now.
if she cant get to see a doctor before her prescriptions run out, i would insist that the doctors who are dropping her give her a refill to hold her over until she can get a new gp. they arent suppossed to just leave you in the lerch. i would make noise about filing complaints with ny state if they dont comply.