Take it from me, you never, ever touch your stepdaughter or let her know you're attracted to her until she first agrees to keep it a secret from her mom. A pretty flaky promise from a teen, yes, but once she's agreed to lie to her mom she'll feel she'll be in trouble too if your wife ever finds out.
What a beautiful girl! She has beautiful breasts and... an incredibly shapely figure. Oh, and he's good at fucking. She is clearly enjoying this vaginal penetration.