Why is this a bad habit? Why are you yelling at her? Why can't she continue with it? It probably feels good to her.
I would guess that she has found out that the spray feels good. That is pretty normal. Point being from many, many other posts on this forum....I doubt that this is a medical issue, but one of feeling good. It is not a bad habit, but a normal one. The standard reply is that this is something that you want to do in private...which she is doing. If you can somehow stop her from using the sprayer, she probably will find other ways to feel good.
But ya, 10 to 15 min. is a long time to hog the bathroom. Outside of setting a timer, I have got no clue on what to do.
Perhaps the book I recommended in your other question might help. And you also might want to see if this one might be helpful.