Sleeping on tummy

I know back is best and you arent supposed to put them on their belly to sleep until they can roll, but the only way my 7 week old will sleep in her own bed is if she is on her belly. I want to transition her to her own bed at night before it gets hard to get her out of my bed. She cant roll but she does have really good head control. She can pick it up and move it side to side while on her belly. So with that being said, what is the difference as far as safety on if she can roll vs her having good head control?