She’s a Siamese chocolate point. In Siamese cats, there is a mutation for the genes of an enzyme (Tyrosinase) that inhibits the production of melanin above a certain temperature. Where the body temperature is lower (extremities, airways), that enzyme is deactivated and melanin is produced, allowing the fur to darken.
Siamese kitten are born completely white, as their temperature is kept high everywhere in the womb, and rapidly start to color after birth.