I'm the mom of a 15 year old daughter and I don't know what all the fuss is about sometimes regarding teens and masturbating. My own mom and I were able to talk about it when I was growing up and I never really made it a secret from her that I did it.
My own daughter and I were having a talk about sex a couple of years ago when she started asking questions that told me she was curious and was looking for answers. She had begun hanging out with boys her age and I was somewhat worried that she may start exploring and I didn't want her getting pregnant and in fact told her so. I was even going to take her to the doctor for birth control if needed, but she assured me that she would let me know if that was something that could happen. In the meantime, I told her that its perfectly fine to masturbate and that relieving herself this way was a healthy outlet. She was open with me as well and told me in fact that she had never masturbated. To make a long story short, we talked about it for a while and then I suggested I could show if her she wanted. We undressed in my room and I showed her where to touch herself and how. No, we didn't orgasm together. No, I didnt use this as a fantasy with my husband or anything like that. Yes, it was a bit embarrassing at first for both of us. But overall it was just what I believe to be a normal way to teach your daughter. She did tell me weeks later, that yes, she figured it out and was enjoying relief from her teen hormones on a regular basis.