I wonder if you could find a Will for Edward Lewis .... to see if a daughter Ruth is mentioned.  That would help!
Looked for an Edward born sometime in the 1780s-1790s buried in Bistre (will start there first).  There is one, who died in 1866... address the Blue Bell, and was a publican.  Lots of my Welsh ancestors ended up being publicans after doing something else - so could be him. 
He did leave a Will, but unfortunately, it doesn't list a wife or daughter as executor!!  Argh!!!
https://probatesearch.service.gov.uk/Calendar?surname=lewis&yearOfDeath=1866&page=8#calendarStill a possibility... but may be a wild goose chase!
You could check for deaths/burials in St. Asaph for Edward of the right sort of age too.  Perhaps you could find a corresponding Will.  
So, chasing down siblings, or parents' Wills doesn't seem to yield a definitive answer 

.  I would suggest you see if you can find some Bistre Monumental Inscriptions to see if any Lewis tombstones there could tell you anything useful.  You might even consider ordering a Will or two - if anything looks likely.  
All I can think of for now...
RK