It is believed the fire started in a property in Castlewellan’s Lower Square at around 4 am this morning.
NIFRS say around 22 firefighters were despatched to deal with the blaze.
Crews managed to pull the teenager from the burning property.
But despite the valiant efforts of NI Ambulance Service staff they were unable to save her.
NI Fire Service Group Commander Max Joyce said that the fire wasn’t flagged up to the house’s occupant as she didn’t have a smoke alarm.
An initial investigation revealed that there was no smoke alarm fitted to the property which could well have alerted her and saved her life.