Firefighters arrived just before 1:30am Saturday and found heavy flames shooting from the roof.
About 60 firefighters responded to the blaze and were able to keep the flames away from the house next door, which was only about three feet away.
The senior resident has lived in that home for 51 years. She believes the fire started in a window air conditioning unit. She said she felt heat coming from the unit before the fire erupted.
Firefighters are ruling the blaze accidental or electrical.
The woman will be staying with family members.