Suggest Treatment For Cellulitis

My 90 year old grandmother has been diagnosed with cellulitis. She was hospitalized for it and given IV antibiotics. Then she had to be sent to a 21 day rehab to help regain strength due to her arthritis setting up. Now the cellulitis has returned (I don't think it ever was completely gone). Is there a type of doctor who specializes in cellulitis and if so, where wouold I find one to take her to?