I found Janet/Jessie in 1911 with her Uncle William and his wife Jessie in Buckie. She was still there in 1921 though this time she was being called William's daughter
You don't say whether William was also surname Robertson? If not - she may have married under his surname
I can only see one possible marriage between 1921-1931
JANET ROBERTSON MALCOLM MACFARLANE
1923 135 / 120 Elgin
Possible death although she would only be 70 in 1971
1971 JANET MACFARLANE aged 71 135 / 369 Elgin