Mary Ann Egan met my Charles John Rowley as they had a child also Charles John Rowley born London Southwark Middlesex 1859 and they didn`t get married untill 1873 in Newcastle upon Tyne as that is where my Rowley`s were living, so i wonder where Mary Ann got to in 1851 census. I might find her yet.
Okay, getting down to business. In 1861 the Rowleys were living at 9 Elswick East Terrace. It's actually just a hop, skip and jump from the Centre for Life

Charles John Rowley Jr was born in Bermondsey, Surrey, registered in the fourth quarter of 1860 (not 1859). This is corroborated by the census entry where he's 6 months old.
Mary Ann's age seems reasonably consistant from census to census. 48 in 1891, 37 in 1881, 28 in 1871, 18 in 1861. However in both 1861 and 1891 her birthplace suddenly switches from Ireland to Leeds, West Yorkshire. Curious...
On the offchance, I tried for a Leeds born Mary Egan of appropriate age in 1851 and
did find one. However the father was one Matthew Egan, which the marriage certificate you have would appear to discount.
I dunno, I'm a bit stumped

She's there from 1861, but before that just disappears. Coincidentally the Mary from Leeds disappears after 1851, but her dad's the obstacle.
Just out of interest, what's the name on the certificate for Charles Rowley's father?