I Wanted to Prank my Step-Sister while Hiding In the Closet but She Starts Masturbating

I Wanted to Prank my Step-Sister while Hiding In the Closet but She Starts Masturbating, I wanted to hide in the closet and prank my older step-sister but she walked in and started masturbating which made things a little awkward. I was going to wait until she finished but then she heard me. How is she gonna react?