Umbilicated is the biggest buzzword for poxvirus molluscum contagiosum. They appear in clusters and are all the same age. It's contagious (she got it from the pool party), and is most commonly seen in kiddos. Can also be seen in adults as a sexually-transmitted disease.

The only other option could be herpesvirus (varicella-zoster), but it would be described as "dew drops on a rose" or "vesicles on an erythematous base" rather then umbilicated.