There was an Ellen Burns marriage in Belfast in 1935, so potentially 'your' Ellen, albeit she would have been only around 17yrs old, based on a 1918 birth. Also one in Craigavon the same year, and one in Larne area in 1937. Remember, though, it is always possible 'your' Ellen took on a different surname if not living with her birth mum.
Another Ellen Burns marriage in Belfast, this time 1941.
For a reasonable cost, you can buy credits and view the marriage details online at GRONI, to see if you can determine if any were indeed 'your' Ellen.