Hiyer,
The front fastening bras aren't to do with size and shape - that is because it can become hard to do up a rear fastening bra after surgery, with a somewhat stiff shoulder and dressing under the arm etc and certainly underwired are a no-no. I did buy front-fastening and found them quite a pain as they put pressure under my arm surgery site as I tried to pull them across the front, but some people get on with them very well, and some prefer to do up the rear fastening type by doing it at the front and them sliding it back round to the back. Some people can't get on with bras at all, and prefer some strong support cropped bra tops. It all depends on what she finds the most comfortable and its worth going along to test some. Some good cheap, very supportive, M and S sports bras would do the job pretty well (the idea is that they don't want the breast moving after surgery). Infact if you go into M and S and explain the situation, they can devote someone to you to advise on appropriate styles. SHe will need to be wearing her bras day and night after the surgery for a while.