Kathy,
It is my understanding that this is fairly common & is caused by moisture
under breasts, such as from sweating. Have her use a cream or powder OTC prep
for athlete's foot. Since I live in Florida, sweating is a common problem that
is responsible for more moisture under breasts than bathing!  (Too much
bathing??? Really!!!!) Since I personally have suffered from excess sweating
due to "hot flashes", I found that the powdered athlete's foot prep was a
"life saver."
Sincerly,
Laura Hart
Winter Park FL-where it looks like we're in for a long, steamy summer!