I believe that Myers is her surname and she was an unmarried mother when Sarah Ellen was born/christened. Whether she married shortly after, or indeed died, I don't know. Equally she could have left the area entirely.
Its one of those where there are several scenarios and may only be proven by some kind of National index search. I could find no deaths for Ruth on 1837 online and so far, in indexes, have found no obvious marriage, thus forcing a name change by 1851.
In an ideal world, I'd do a national search on the 1851 census for all women with the name Ruth aged 19-21 and born in Fordon/Hunmanby.
I can but dream!