It probably wouldn't be easy to find many Essex songs that would work for you (just as there are not that many Devon songs which work for me) - it's unlikely that you'd find all of them to your taste or whatever, but you could widen it to, say, East Anglia, which would give you a much bigger pool to dip into.

As to the Leigh FF, the lady you're thinking of may be Kiti Theobald, who is a fine singer (in fact, one of my favourites) of traditional songs, but not what is generally thought of as a traditional or "source" singer.

Barbara