Hi
The IGI has Ellen Morrissey, born circa 1850; married James Power at Clonmel in 1871. (If you don't already know about the IGI, 'submitted records' should be treated with caution as to their exact accuracy).
I have a Mary Ellen Morrissey in my family tree (who married a Butler), and you're right, Morrissey is a familiar surname in the Clonmel area and neighbouring parishes into co.Waterford.
Some of my Butler records are in CLonmel, but they were actually born/married in co.Waterford just over the border.
(Sorry if the IGI stuff is something you already knew!)
Cheers,
Mags