Flames erupted on the 600 block of Sussex Road.
Fire officials believe the woman, who is in her early 70s, was among those who called 911.
However, she passed out before she could escape.
"Our first company arrived at heavy fire in the back of the building. Crews went in and did an initial search and found a resident inside," said Lower Merion Fire Chief James McCoy.
"Personnel had to go in and remove her from the house. She was unconscious at the time," said Narberth Ambulance Deputy Chief Patrick Gwynne.
Chopper 6 over scene of fire in Wynnewood, Pa.
She was rescued from the blaze and is now in critical condition at Jefferson University Hospital's burn unit.
Several neighbors reported hearing an explosion as well. At this point, investigators believe that was a propane tank from the backyard grill that detonated.
Officials also say the explosion was likely the result of the fire, not the cause.
The cause of the fire remains under investigation.