Thank you for visiting the family practice forum.
Well, Roseola is possible but what really comes to mind given the history you describe is an infection known as "fifth's disease" (erythema infectiosum). This is caused by a virus and is associated with a rash on the face which later spreads to the extremities. It is made worse by warmth.
A scarlatina rash is another possibility. This is diffuse almost "sandpaper like" rash that is present in patients with strep throat. Since she has a sore throat as well, this may be possible as well.
Allergic rashes are another possibility, but far less likely as allergic rashes are not typically associated with fever.
She obviously needs to see a doctor to be examined.
I hope this proves helpful to you!