When can baby sleep on tummy and with blankets?
My baby is 4 months old and has just now started rolling over from her tummy to her back. If, in the middle of the night in her crib, she rolls from her back to her tummy, and stays like that, is it safe? How about when to put blankets/pillow in her crib? She has VERY good neck support by the way.

My ped said it is safe once they can roll over on to their tummy themselves. You should still put baby down on her back, but if she rolls it is fine to leave her as is.
As for pillows, blankets etc. As with most things, wait until 1 year.
Once they can roll over they are fine to sleep on their stomach.
As for blankets, I would stick with sleeper-sacks or something similar until at least a year.
I had both of my babies on there bellies by 2 months, they just slept better. The baby should be fine on its stomach as long as it has a little control of its head. As for blankets, they made me nervous. I dressed the baby in blanket sleepers at night that way you have no worries and they are warm.
If she can roll over and she rolls over onto her stomach on the middle of the night , you can leave her on her stomach. Now for pillows, blankets..etc..You definitely can’t use them now. It isn’t ever safe to give them a pillow in the crib or a blanket. Once they get moving they can wrap themselves around the blanket. When they are in the toddler bed then you can. You want to do everything you can in your power to prevent SIDS.
my son starting doing that at 3 months and his doctor said that it was fine for him to sleep on his stomach once he rolled there his self and i put a blanket on his back and normally he wiggles out from under it but i never had a problem with him sleeping that way and hes 10 months now
My boys slept on their tummies at one month, they just slept more comfortable that way. AS long as the baby has good neck support and control it should be fine, jus ttry to avoid having too much in her crib, one blanket should be fine.