Rash from diapers

My sister lives in a long term care facility and wears institution-brand adult dapers. For many months she has a terrible rash with swelling, burning and open sores both internally and externally. Doctors have tried many creams without success. Her family is wondering if this might be an allergic reaction to something in the diapers the nursing home uses. Are the Depends brand hypoallergenic? Have you heard of a problem like this from others who wear protective underwear?