Nia the phoenix girl.

Actually over 2000 years old, but usually looks about eight to twelve. Rarely over sixteen or eighteen.
She has a tendency to burn herself when people get hurt. Ingesting her ashes (gen. mixed w/ water) will heal nearly any injury, with the side effect of causing her to regenerate at a physically younger age proportional to how many ashes are left (ex: if she's sixteen and someone drinks half her ashes, she'll come back 8.) This is why she usually looks like a kid.