Dear Lani,
Because she is healthly and strong enough to raise her chest up on her hands, don't even give it another thought. My little guy, Matthew (now a very healthy 2 1/2 year old) was so much happier on his stomach that I left him there when he would roll, and then I started putting him down that way. I worried for a while, but he really did sleep so well and woke up rested. Once he pulled the blanket over his head. He cried and when I got there he was all sweaty and out of breath. That convinced me that if he was having trouble breathing, or just uncomfortable, he would let me know. If your little girl is tired of being face down, she will wake up and call for you. And, as my mother-in-law always reminds me, when we were babies we were always put down on our bellies, and we have lived to tell about it.
K.