Liberton Kirk Session Records 1639 - 1990, Liberton 22nd Jan 1826
It says................
"The session being met and constituted accredited Minister and Elders.
Robert Groserd an unmarried man at Westedge, appeared and declared that he has had a child by Margaret Irvine an unmarried woman lately residing at Gilmerton. He was rebuked and absolved. He gave ten shillings to the Poor,
Concluded with Prayer."
Unfortunately these Kirk records do not give the names of the children BUT there were no further entries of any other children born to these parents through to 1835. (Robert & Margaret mar in 1832 and their 1st recorded child was born in 1834)
The above entry therefore looks like the child must be our Isabella. It would also explain why Isabella was not with the family on the 1841 census as she would have been abt 15yrs old and already working.

July 1876 - Isabella dies at 21 Kirkgate, Leith. Her son Robert is listed as the informant of death and residing at same address. John is shown as wood sawyer on Isabella's death cert and was still alive, why was he not the informant ? There is a side note on Isabella death cert which I think says
see "register of corrected entries" Vol 2 for ? 191 ? July 25th 1876  (not sure if this is relevant or not)
NEW INFO (Feb 2009) I have now been able to access the RCE pg 191
and it has corrected -  her name to include her maiden name, " Grosset"
                              - her age as 52yrs instead of 51yrs and address as 12 Kirkgate instead of 21
                              - cause of death as "diseased condition of the heart as a result of a post mortem examination
and signed and dated August 5th 1876 by the Procurator Fiscal.