I was going to say the same as HotI, it'll be hard to stop her and it may just be the surprise of waking up that way. When DD learnt to sit she'd wake up in a sitting position and start crying, same again when she learnt to crawl. It just took time for her to get used to it and either stop doing it or get back to a comfortable position.

I think if you were to tuck the bottom of the sleeping bag under the mattress she'd still roll because it wouldn't actually hold her in position, and then her legs would be twisted or more held down, she'd probably like that even less. Does she maybe not like it because she's wrapped when she rolls? Maybe it'll actually be better in the sleeping bag?