Agreed with the above to try loosening / alternating and making sure she’s not too hot. I always used to get this on my wrist when wearing a Fitbit but assumed that’s because I was working out / getting a sweat rash under the band. It cleared quite quickly
Could be on too tight or she’s too hot and that’s why it’s causing irritation. I swap which foot I put it on every night and I only put it on once my baby is fully asleep and I’m leaving him in his room. Works for me as he doesn’t wake up to me putting it on I know may be different for others x