Depending on just how busty she is, plate armor might not be an option. Soft armor would be able to conform to her shape a bit, but would offer far less protection.
Are you looking at plates or just a kevlar weave? Safariland makes the Savvy line, which is specifically formed for women.
EDIT: If you go with plates, you can just get a carrier that's big enough to fit over her breasts and add foam padding to the midsection. That should make the plate lay flat.
Last edited by db42; 12-18-2012 at 8:46 AM..