Your daughter is big enough now that she will lift her face if she can not breathe. Once they can roll on their own, it is fine for them to sleep in different positions. My son is on his back, stomach, side, back, etc...all night. He is a big mover. I was scared when he first started sleeping on his belly too, but we can't keep them on their backs forever
I have the angel care monitor too and it helps me sleep better at night.