I have a problem

My little girl is 6 months old. She has slept 12 hours straight since birth. I decided to start transitioning her to non-swaddling, but when I keep even one arm unwrapped, she rolls onto her belly & screams. Whereas when she’s fully swaddled, she doesn’t roll at all.

I’m at a loss on what to do. I want her to sleep through the night, but it’s been recommended that I stop swaddling.

Any tips?