We have the same issue. Change each side you feed her on, how you hold her. Lots of tummy time. I also have increased contact naps in the day so she's not on her back so much. We've also seen an oestopath so help loosen the muscles to help my little one turn her head
My daughter who is nearly 9 weeks has a preferred side too. I saw a physio about another issue for her but they suggested when you have her in the pram or napping in the day so they’re supervised to roll a blanket and place it next to her head on the side they prefer so stop them going the whole way. Obviously you need to supervise them with doing this. Also feed from both sides and use toys to get her to follow and try and turn their head. We also put sensory cards on the wall by her changing table as that was her non preferred side and she’s now looking at them. It’s taken us time but over the last few days she’s started to turn and lay with her head both sides. Xx
You could probably use them in the day as supervised naps but I wouldn't do it off a night xx