The 82-year-old was at the property in South Beach, Troon, when she was threatened by a man who demanded she hand over money. He got away with cash and items of jewellery, many of which had been gifts from relatives.
Police in Ayr have launched an investigation into the incident, which happened at around 8pm on Monday, and have issued a description of the suspect.
Inspector Stevie Wallace said: "We are in the process of reviewing CCTV images and are determined to trace the man responsible for this crime.
"Anyone who preys on our elderly members of the community is a coward. Many of the items stolen were gifts from family members and the victim is desolate at their theft."
He appealed to anyone with information to get in touch.
The suspect is described as white, around 6ft 2in, with cropped, short dark hair and a stocky build. He has blue eyes and speaks with a local accent.