Get a plug retaining harness for her.
Seriously, I bought one for my then GF and kept it after we broke up for those occasional forays into something a little kinkier.
They look sexy as hell and they work. And right now until April 30, they have free shipping.
http://www.northbound.com/Northbound...=CY4&S=&RegId=
Oh, and Northbound is definitely high quality high end stuff. No cheap crap.
Check out their leather bras for her.