The best thing you can do is be there for her. Be there for here in the way she wants you to be. Learn her trigger signs, help her monitor herself.
Things always seam worse at night. Find out about your local metal health team and their out of hours service, it may be based at and A&E in the areas. It can be hugely valuable, for both you and her.
Unfortunately be prepared to get hurt. She will not mean it, she maybe has no control over it but it may happen. You need to know how to look after yourself, do not bottle things up. Find someone to talk to there are several support groups out there for you and her.
This page has some great links
http://www.bbc.co.uk/health/conditions/mental_health/index.shtml especially this one
http://www.mentalhealthcare.org.uk/
I don’t want you to get a negative impression, just to get some tools to cope. I am not claiming to be an expert I have some expereince in the past and if I had know some of these things then I might have been more prepared to help and cope. PM me if you need more info, help, an ear.