L.G.
Don't worry, soon enough she'll figure out how to roll back over or she'll find she actually likes being on her belly and that will stop. It's a short phase that all babies go through. Don't be surprised if she also goes through a period of getting her arms/legs stuck outside the bars on the crib and can't figure out how to get them back in. That also doesn't last too long, but sometimes they get really stuck. One of my girlfriends had to use a baby oil to free her daughter's leg! Good luck!
L.