I just have a layperson's comments, but I have had mental problems of all sorts from a bad car accident. She's not acting, rather she is sick. She should be in individual psychiatric counseling, aside from the family counseling and aside from what she's getting in the facility. Also, the seizure medicine she's taking is NOT working and most definitely needs to be changed FOR SURE. Also, she should perhaps be on short-term tranquilizers, strictly controlled by a psychiatrist... and don't let them give her SSRIs, they're too strong for a young person. An endocrinologist has got to run some thyroid, adrenal, and ovarian panels to see what her hormones are doing, too, could be she's got a couple things going on at once, rather than only a seizure disorder. Also, blood should be drawn to see if she has any metals poisoning or vitamin deficiencies.
She should be put in an exercise programme of some kind, be it running around a track, or swimming, or learning horseback riding, tennis, anything that will wear her slam out on a regular basis. In addition, get her into a creative class of some kind, be it learning to play guitar, art is especially VERY good for people whose minds are confused (anybody can slosh some paint around), and giving her nonfiction books on stuff like dogs, home design, movies, musicians, stuff teens like or that you know she has an interest in. This thing has to be approached in a holistic sort of way, where you throw everything at it, instead of just one or two changes.
Under NO circumstances should she be in your home because of the scissors thing, so keep her in SOME sort of facility for maybe as long as six months, to a year even, be it where she is now or a private type place if you don't like where she is. Her life needs to be continuously monitored, she needs to be physically and mentally engaged, whilst allowing for relaxing pursuits, and her health in general needs to be really checked out, and she needs the right meds, and while all this is going on, she could keep up with schoolwork with a tutor if necessary. While it will take some energy from you and your husband, I don't think this is a conscious thing in her at all, rather I believe she's quite ill and has no control over it, so she needs your help. People get sick all the time, so if you look at it that way, I don't think you should feel too badly about this, and eventually she and you two will pull through.