Well, I'll weigh in on this from the other side.....I am large naturally and often very sensitive due to my cycle....
I currently use the SmartVest by Electromed - I still have an older model Thearpy Vest (HillRom at one time, but I think they've been sold again).
The SmartVest wraps around the body something like putting a coat on. The other one I wear backwards as where the hoses 'enter' it are right square over the boobs for me and the majority of the percussion is on breast tissue - even when I'm wearing a bra. Electromed is much more comfortable and I can move the puppies up and out of the way when needed. I'd encourage her to look into their product first.