crohns and vaginal burning

my mother, 76 wiht crohns has developed the symptons of a yeast infection, she assumes caused by leakage from the bowel. She has been tested fro yeast infection and it came back negative. They gave her antibiotics. They worked for about 2 weeks. the condition has returned. Panty shields do not help.Tried different soaps, no soap, acidoplolis, change of diet, nothing seems to relieve the burning of the labia,,,any suggestions?