What to do about my step-daughter?

My wife's daughter has been teasing me a lot lately.. Coming out of the shower undressed, walking around with these little tiny shorts on, and she has a perfect round luscious for only 15 years old. I know, I know, I am really asking for trouble but I can't help but see the way she looks at me. And just the other night when my wife fell asleep on the couch her daughter put her feet on my lap and my got so hard. HELP!