A belt system is the way to go, for sure. Another option is a bandolier, which then separates teh boobs to make them more pronounced for distraction purposes.
You can also wear a low hanging chest rig, that is more of a stomach-rig. I usually wear my chest rigs loose and on my belly. Some Russian vests do that quite well,
http://www.srvv.org/en/catalog/1319/29233/Belt setup. If she needs more space, add some droplegs.
Another option is a backpack with a MOLLE cummerbund, that has mag pouches on her sides.