IS there something that could be going on with her?? That she doesn't want to be alone?? Maybe leave the light on, get a night light or something??
It sounds like she is afraid, and this needs to be addressed. Ask what is making her afraid, talk to her about it. For her to want to give up everything just to sleep with you says something has really scared her, and you need to know what this is. She may have seen something on TV, or been told something at school, you just don't know. When things like this happen out of the blue, there is a good reason at this age.
She's not doing it for any other reason, so I wouldn't punish her, she can't help that she is scared. If talking this over with her doesn't help, try leaving a small light on, or some very soft music, or both. Maybe spend a night in her room with her to see if there is something like a tree branch rubbing against the outside of the house that is scaring her, just any odd noises. As adults we hear things in the night that will make us get up and check them out, she can't do this so it's off to mommy and daddy who she knows will keep her safe. You just need to find out "why" she is afraid to be alone and go from there. She doesn't want to be up any more than you do, but if she is scared she can't help it. Good luck and take care.