Stomach Sleeping

My 4 month old (19 weeks) has decided that she wants to roll over from her back to her belly whenever we put her down for a nap or for bedtime. I’ve read that as long as we place her in the crib on her back initially and then she rolls to that position on her own it is safe. I’m a first time parent and SIDS is terrifying to me, and just want to make sure little one is okay to be sleeping like this, or if I need to stay up all night and keep flipping her to her back.