My 9 year old sister won't brush her teeth no matter what my mom and I do! (More details inside)?

take her to the dentists and have him/her do a deep clean on her teeth...it is painful, but beneficial. Also they have a way into scarring kids to brush their teeth. If she didn't like the feeling of the deep clean...keep reminding her that she will have to do that every year is she does not take care of her teeth properly.