Grandmothers Perm Didn't Take?

My grandmother got a perm it didn't seem to take. Her hairdresser has given her them before and they have been beautiful. it didn't take and she told her it could be due to some of the medication she is taking. How can I find out if the meds she takes is causing her resistance to the perm. I've googled but haven't found much until I came across your site.

Thanks