Sue:
So sorry to hear of this. Am hoping your granddaughter will be found safe and returned ASAP. It does sound like she needs intensive treatment with someone experienced with this type of problem.
My youngest sister had some behavior problems growing up. First-grade teacher hinted that she was brain-damaged (not!). She hated going to school, had stomach aches, other ailments. The summer before her senior year in high school, she was finally DXed with a learning disorder and put into a special program -- did not have to set foot back in the school -- and she did graduate. She "ran" away from home at age 16 -- got up in the middle of the night and drove from Dallas to Austin Texas in her Ford Mustang. Just left a note on her bed that she wanted to go see a friend who had moved to Austin. (I heard about this months afterward.)
Eventually, she straightened up and went on to a medical assistant school, then an LVN program and eventually went on to a community college for her associate degree and became an RN. She worked on her RN while taking care of two children and being a housewife. She aced the nursing courses. She's darned smart; as a child, she just didn't learn the way they wanted her to!
She didn't put up with anything from her kids. She's a great mother, grandmother, etc.
So -- I'm hoping that perhaps your granddaughter is a little like my sister and that help can be found for her..