M.F.
She will eventually learn to either roll back over on her own or learn to be okay sleeping on her tummy. If you go in to roll her over when she crys, she won't learn to self-soothe and simply be okay however she's laying. She'll only learn that tummy=cry=Mommy to the rescue. You should still lay her down on her back, but if she's rolling over on her own, she's okay to stay sleeping on her stomach, so don't feel you have to roll her back over for safety.
PLEASE do not use any kind of prop or wedge or anything to keep her from rolling over at night. Since she is rolling over on her own, anything but a light blanket in her crib is a smothering hazard and shouldn't be in bed with her. Recently, sleep positioners were recalled due to smotherings and it was recommended that NO sleep positioners should be used in any way, shape or form in cribs.
Let your daughter figure this out on her own and it will be the safest and best solution to this very common problem at this age. Good luck!