Baby is scratching herself

The past week my husband and I noticed scratches on our little girls leg, and only her right leg. We at first thought it was possibly my wedding ring, that was somehow scratching her on accident while I am feeding her. I have been keeping my rings off but it kept happening so then we thought maybe our 4 year old was accidentally scratching her. We watched closely but our oldest was not doing anything to her. Well this morning when I got up to feed her she was having bad gas, I noticed she was wrapping her left leg underneath her right and it looked like it is her toenail from her left foot scratching her right leg like that. I feel so bad because it looks painful, but it doesnt seem to effect her. I just feel bad that I did not notice her doing it before and how to get her to stop when she does it while she sleeps 😭