I have seen it when I worked on a psychiatric ward. The person will be in a frozen statue like state which could continue for a short or long time. It is usually treated with something like Lorazepam which will help the muscles to relax.. Is she in hospital? If it is the first time it has happened I imagine it will be very frightening for everyone involved, excluding staff if she's in hospital.. if you visit just show respect and understanding of her condition it is not possible to cajole someone out of it..
