Just to add having read AMS post...there are some great sites online where you can buy post mastectomy bathing suits. Getting a well fitting prosthesis is important if your wife is concerned about having one flat side (some people couldn't give a hoot and more power to them). You can swim in the good quality ones no problem and they are good for every day wear. The better the quality, the longer they last and the more comfortable they are.
On the issue of flying with expanders (the 'first' implants they put in to stretch the skin in a 2 step recon.) - never heard of this being a problem *except* from personal experience, because the port they inject the saline into is metal and can set off the metal detectors so good to warn the TSA...