I don't know if you went any further with this but it seems that there were two Ann Greggors, both married in 1820.
The first married James Barr 38 Feb 1820 in Braddan. This was the mother of Mary Ann Barr who appears as Mary Ann Kissack with her parents in the 1851 census. She married John Kissack 21 Nov 1850 Patrick.

1851
Duke Street
Ann Barr abt 1803 Peel, Isle of Man, Isle of Man Wife German Isle of Man
James Barr abt 1804 Ireland Head German Isle of Man Musician
Sarah Barr abt 1834 Peel, Isle of Man, Isle of Man Daughter German Isle of Man
William Barr abt 1839 Peel, Isle of Man, Isle of Man Son German Isle of Man
Mary A Kissack abt 1827 Peel, Isle of Man, Isle of Man Daughter German Isle of Man Dressmaker

The second, so far unidentified, Ann married John Corlett 5 Nov 1820 Ballaugh. The family are in Malew in 1851.

1851
Cottage Garth
John Corlett abt 1791 German, Isle of Man, Isle of Man Head Marown Isle of Man Chelsea Pensioner
Ann Corlett abt 1799 Patrick, Isle of Man, Isle of Man Wife Marown Isle of Man
Ann Corlett abt 1844 German, Isle of Man, Isle of Man Daughter Marown Isle of Man
Christopher Corlett abt 1835 German, Isle of Man, Isle of Man Son Marown Isle of Man Lead mines labourer
Edward Corlett abt 1841 German, Isle of Man, Isle of Man Son Marown Isle of Man
Philip Corlett abt 1838 German, Isle of Man, Isle of Man Son Marown Isle of Man
Eleanor Bridson abt 1775 Patrick, Isle of Man, Isle of Man Aunt Marown Isle of Man

I hope this goes some way in helping to sort this problem out.

Jane