If she's busty a plate carrier will prettymuch be a no go.
God blessed my girlfriend with a pair of 32 GG's, well not really, she's 5"6' and 112 pounds, skinny girl huge chest, but I'm not complaining
even though she will from time to time lol. unless you take out the SAPI plate it wont fit comfortably,
however my TT two piece MAV fit's perfectly. anything that sit's on the stomach will work just fine.
and don't get the corset dude, she'll think she's doing this for some sort of sick sexual preversion of your's and it will be demeaning, not to mention girl's can't really breathe or move in a corset.