Originally Posted by Charlatan

Buy and leave it on your dresser in plain sight.

This way you aren't hiding anything. Then if she asks about it tell her it's your sex toy.

Barring that, put it in your sock drawer. If she finds it it is up to her to ask you about it and explain why she was snooping in your room. If she is offended by your sex drive ask her if she would prefer it if instead you brought home young men or women to help you out. That way you wouldn't have to use a silicone friend.