Did you ever get any further with your Monaghans in Ireland?
I have a Mary Monaghan from Galway in my tree born c1821 (give or take a decade -

). She married a man name Darcy/D'arcy and they had two children in the 1840's (Mary and Ann). But I think he must've died (can't imagine a divorce somehow) and she married a Thomas Berry and moved to Liverpool c1850 where they had 3 more daughters. She died in Liverpool in 1885.
I can't get back further with my Monaghans, so I'd be interested in any suggestions you might have.
Regards
Ann