i dont think you have to worry. probably allergies....... or maybe a shower is needed
It could be an infection, maybe from a bug bite or something like that. But sometime after squeezing something it causes some swelling its the bodies natural way to protect itself. but i would take her to get seen , a 4 year old dont normally get pimples so it could be something your unaware of.
Squeezed it? Please get her in to see her pediatrician or emergent care asap if this has not subsided.
If there is still swelling it's probably a good idea to get her to a pediatrician.