what is this rash about

Since you mentioned vaccination was last Friday, some vaccines can cause a rash several days later, depending on which vaccine it was, though it's impossible to say from the photo whether that's the cause. I'd keep an eye out for any of these: -Fever or your child seeming unwell -Swelling of the lips, face, or eyes -Difficulty breathing -The rash turning purple or not fading when pressed If any of those happen, or if the rash is spreading quickly, I'd get her checked by a doctor today. Otherwise, it may be worth sending a photo to your paediatrician or visiting a clinic, especially since it's her first time having a rash like this. Hope your little one feels better soon ❤️