Diaper purchasing for adult?

My sister and I have been supplying the diapers but we are having problems purchasing diapers they are very expensive. She doesn't have Medicaid, not eligible.
She's eligible only for Medicare, but they don't pay.
I am looking for grant or program to subsidize the diapers. She's 90 years old we are trying to keep her at home she is also living with her husband he's 91 years. Any thing you can do greatly appreciated.