as a cutter i know what it is like for family to find out.
The best thing to do is say that you are there for her and will help her.
Ask her if she would consider counciling or therapy and just support her as much as you can. You should tell her grandparents to just look after her and not treat her any differently.
Meg.

Cutting is part of a disorder call borderline personality disorder. It's a complicated disorder to treat and needs to be address usually by intense therapy with a therapist specializing in this area.

This person tends to be called an attention seeker and will do things to draw attention to oneself. Their moods can become extreme from acting depressed to very angry outbursts. They tend to over react to events around them and constantly seek and cause drama all the time.

It's not that they sit there in the morning and decide...ahhhh, what can I do today to cause all heck to break loose....it just take over.

The usual cause of this disorder is physical or mental abuse, rape or a traumatic even in their life. You said that your daughter is living with her grandparents and you are not allowed any contact with her...why is that? Sounds like you found the root of the problem.