Allergic reaction?

I know no one can diagnose a rash through a picture, and if it doesn't go away I will make a dr appointment. We gave peanut butter for the first time monday and yesterday, and then early today I noticed this on her upper thigh. I don't see it anywhere else on her. I was super scared to give peanut butter in case she had a reaction to it. If it was from the peanut butter it would have probably showed up the same day right? And what be moreso hives? Has anyone else's LO had a spot that looks like this?