I usually allow it if I am asked before someone uses my photos. Asking afterwards is very disrespectful and I think you have to learn that you have to respect other people works. If I let you go with this, you'll probably do it again in the future so tell me if there's any reason why I shouldn't say that you have to remove it. If you can tell me a good reason then I think I make an exception and let you have it in your gallery.
wow that's a bit rude :'O I mean she took your drawing as a reference because she loved it, drawing it is a form of admiration of your art. Even though I see your point, you shouldn't be disrespectful yourself and blame her. She told you that she used it and gave you reference. In a way that could make your photo more recognized as well.