Depends largely on why she's getting up. Is she coming to your room? Does she get frightened? Have bad dreams? Is she just not tired? Most of the time, there's some reason (other than just doing it to tick you off). Things to help soothe -- nightlight, ritual of "getting rid of the monsters" before leaving her room, saying bedtime prayers after she's tucked in, a little pen light under her pillow -- often ease the loneliness and fear. Also, how old is she? That will dictate a lot of her reasoning capabilities, both on why she won't stay in bed, and how you can best cope with it.
If she just doesn't like being in there by herself or is bored, it sometimes helps if you can make it desirable to be in bed. Let her know she's going to be needing to stay in her room, and let her pick out her comforter and sheet set so she'll feel like she chose her surroundings to some extent. Maybe get one of those gausey drape things that you have from the ceiling that go over the bed like a princess would have... those are like $20 at a bedding store.
You could put together a reward program, so if she stays in her room until morning, she gets some small reward. Just be careful not to bribe. Setting up guidelines ahead of time (on nights when you stay in your room all night like a big girl, you can choose what you want for breakfast the next morning) is very different from bribing (I'll give you xyz if you go back to bed and stay there). Maybe even do it like some people do potty training and make a sticker chart with a sticker for each night she stays in her room. Then for every week with a sticker for every night, a small stuffed animal to decorate her bed.
Hope this helps a little.