Hi, Pleiades-
I am a breast cancer survivor and opted to have a bilateral mastectomy with saline implant reconstruction as part of my treatment (I was in my early 30's and did not want to take the chance that I might get another tumor in the other breast...but that's another story for another day). In other words, my implants lie under my skin and muscle, but I no longer have breast tissue covering them, so I guess you could say my implants are more unprotected than hers would be, assuming she had augmentation and not reconstruction. I had my last surgery in February 2004 and have completed probably close to 50 dives since then - in all kinds of conditions (i.e., we went to Utila and did about 25 dives in April, and I did a 2-tank boat dive last weekend off Cape Ann in low-50's water w/drysuit). I have had absolutely no problems, and all of my doctors know I am an avid diver. They were intitally planning to do silicone implant recon, but the implants weren't available at my hospital at the time I had my surgery, even for reconstruction.
I have the OK to do specialized stuff as well - including deep dives (out of recreational range).
If your friend is still concerned, she should contact her plastic surgeon and ask whatever specific questions...but please reassure her that she can feel pretty confident that it is quite difficult to rupture an implant. My plastic surgeon told me that she has actually jumped up and down on one of those suckers, and it was just fine.
If you have any other questions, please feel free to PM me, OK? Good luck!