Hi, dad daughter question please, my daughter Leona is 13 and spends most weekends with me, I have a hot tub in my conservatory and she always asks for us to go in it together. It isn't long before she is facing into one of the jets as she chats away and by her conversation I know she spends the whole time on the edge of orgasm. When she eventually gets out her bikini is usually ridden right up her swollen vagina, I have snags getting out because ashamedly I am aroused during this.
You are the dad and she should not be surprised when you tell her what to do. You ought not bathe with her when she is masturbating. I would suggest telling her to do that when you're not around, and better yet, advise her that masturbating with water jets is bad for her developing sexuality. Girls who learn to masturbate with the gentle touch of their hands have an easier time reaching orgasm in intercourse. Please suggest she read http://www.healthystrokes.com/female.html
And if she persists, just leave when she starts.