Let baby sleep on her tummy?

She will be 6 months in a few days, she can roll back to tummy no problem but cannot roll consistently from tummy to back and has only done it a handful of times. I have her in her own room and in a crib with nothing but a fitted sheet. She sleeps in a sleeper and her zippadee zip. If she rolls onto her tummy during the night can I leave her to sleep this way? I’m very nervous. This is the first time she has actually rolled onto her stomach to sleep and I cant help but stare at the monitor. She seems comfortable but is it safe at this point??