Documentation that I have seen to the contrary (for example, J T Clay's family group sheets, based on family oral history and they 'should' know: she was his great-grandmother after all!), Ada Lucinda Watson would seem to be the Issac Jason WATSON's daughter by Louisa DENT, not Elizabeth DARNELL. Otherwise, all the known dates are wrong.
For example, the 1870 Census (Austin Co., Texas) states that Lucinda was 30 years old and born in Missouri. However, in 1840 Jason Watson's family was in Attala Co., Mississippi. (see Rose-Stroud [http://awt.ancestry.com/cgi-bin/igm.cgi?op=GET&db=:1461169&id=I103]) and he was apparently married to Louisa Dent at the time.