Now that she's rolling - how do I stop her!!!?????

I'm finding her rolling in her cot after her nap, or like today - before her nap as she won't sleep.
She does it with her sleeping bag on and just now I tried wrapping her (which we stopped at 8 weeks) in a light sheet and she managed to get it off and get her leg caught between one of the gaps in her cot and the wall. It wasn't stuck because the gap is wide- but she's not that mobile yet that she knows how to get out. She's so tired but keeps rolling over then cracking it because she's on her tummy.

What can I do, if anything, to prevent her getting hurt or ending up under covers etc???