You said the marriage took place at Mullyglass but wasn't sure where the couple actually lived. Which church was it?
Think the townland might be Mullaghglass in Ballymore civil parish, Banbridge Poor Law Union which is actually in County Armagh. It's only about 12 miles from Gilford.
There certainly were Napiers in Mullaghglass- see Will Extracts at
www.proni.gov.uk (Sarah's Will available to view)
David Napier, Mullaghglass died 26 February 1909
Sarah Napier, Mullaghglass died 7 December 1914 (widow of David)
Joseph Napier, Mullaghglass died 25 September 1937
Added- David & Sarah Napier also had a daughter Jemima so perhaps a family name?