If Janet (b.1775) lived till she was eighty, then her death would have to be recorded in the new Register of BDMs that came into force at the start of 1855. If so, that would disclose her mother and father's names. It's a long shot, but that's how I found the name of my great great great great grandfather Teárlach MacAllister's wife - one of his daughters, born in 1772, lived until 1870, so her parents' details are recorded.
I cannot find any trace of a marriage for *your* Janet McLeod in the Durness records though - there are two other Janets, one in Sango, who married Murdo McPherson in 1790, was widowed, and remarried the scooolmaster John McDonald in 1800. Janet the daughter of Neil is too young to have married in 1790, so this Janet (daughter of Donald) seems to be an aunt or older cousin. The only other Janet McLeod is in Achunahanait, on the opposite side of the parish, a good two hours walk from Sangobeg in the days when there were no roads on that side of the village