Sarah McCombish/McComish/McCrombish

Sarah was my 3xGreat Grandmother. She was born in Ireland around 1791.

I know very little about her other than her parents were Barclay McCrombish and Bridget Rafferty.  I am having trouble finding any records of her under a variety of surname spellings! 

Sarah married John Coventry (from Dunfermline, Fife, Scotland) in County Tyrone about 1813 and had two sons:

Thomas b: 1814

John b: 1816

Both sons were apparently born in the Army barracks in Tyrone.

Sarah and John were living in Scotland by 1818 as their daughter Elizabeth was born there.

John Coventry was deceased by 1851.

On the death certificate of son Thomas (who emigrated to Australia in 1846), his father John Coventry is listed as a soldier.  Was he perhaps was in the Scottish militia?

On daughter Elizabeth's death certificate, father John is listed as a lighthouse keeper.

There is a possible record for Sarah's mother under the name of Brigetta Rafferti (with Brigetta's parents listed as Jacobi (James) Rafferti & Maria (Mary ) Cormick.)

I am having trouble finding out anything more about Sarah and her family and why husband John Coventry was in Co Tyrone at the time.

Any help would be much appreciated!