I take it that this is Isabella McLachlan, born 30 November 1863 in Knockando? Have you got her birth certificate? If not you can view it at
www.scotlandspeople.gov.uk. At what address does it say Isabella was born?
The FreeCEN transcription lists at Croft Stewart, Knockando in 1871 Alexander McLachlan, 63, mole catcher, born Kingussie; wife Margaret, 66, born Inveravon; daughter Margaret, 35; grandson Peter Davidson, 13; granddaughter Isabella McLachlan, 7; granddaughter Jane Grant, 3; all born Knockando.
In 1861 at Knockdow Alexr McLachlan, 53, ag lab, born Kingussie; wife Margaret, 56, born Inveravon; daughter Eliza, 30; son Wm, 12; grandsons John Smith, 6; Peter Davidson, 3 and Alexr Innes, 3; granddaughter Margt Innes, 1; all born Knockando.
In 1851 at Croft Stewart Alexander McLachlan, 43, labourer, born Kingussie; wife Margaret, 46, born Inveraven; daughter Jean, 10 and son William, 2, both born Knockando; boarders Jessie Grant, 7 and Peter Grant, 4, both born Grange; mother-in-law Helen Black, unmarried, 78, born Inveraven.
In 1841 at Croftskavart are Margaret McLachlan, 36; Jean, 8; Margaret, 6 and Bell, 2, all born Morayshire. Betty McLachlan, 11, is a female servant at Robertstown in Knockando.
You can look at the full transcriptions of all these at
https://www.freecen.org.uk/cgi/search.pl and the originals at Scotland's People.
So assuming that their ages are accurate, Alexander was born in 1807 or 1808 in Kingussie, Inverness-shire and Margaret was born in 1804 or 1805 in Inveravon, Banffshire, the illegitimate daughter of Margaret Black.
From the deaths index at Scotland's People, Alexander McLachlan, aged 81, died in Knockando in 1889. Margaret Black or Grant or McLachlan died in Knockando in 1892 aged 87.
You should go to
www.scotlandspeople.gov.uk, invest in a few credits, and use them to view the death certificates. They should tell you the full names of both parents of both Alexander and Margaret.
What is your evidence for Margaret McLachlan being born at Knockehillock? There are six children of Alexander McLachlan and Margaret Grant, all baptised in Knockando. You can view all the baptisms at Scotland's People. One or more of them may tell you where the parents' residence was at the time.
You can see where Croftstewart is on the First Edition of the Ordnance Survey six-inch map - see
http://maps.nls.uk/geo/explore/#zoom=16&lat=57.4640&lon=-3.3122&layers=5&b=1Betsy may have married a Robert Ross but according to my now deceased mother, Isabella, Betsy's daughter, was known as Isabella McLachlan or ROBB...not Ross.
So maybe her father's name was Robb. Have you got Isabella's marriage certificate? Does it say who her father was?