Rashes on ankle 4 month old

A few of us in my mum group have had babies with rashes at that age and honestly it can be so hard to tell just by looking what the cause is. It might be good to bring her to see the PD soon, just to be safe, especially since she is only 4 months old and her skin is still so sensitive. One of my mum friends always says for anything on the skin at this age, better not to wait and see too long. The PD can check properly and advise on whether it needs any treatment.