On the LDS IGI site you can search for Christian names , so looked for any Lydia born IOM 1790 to 1800 and got a blank.
Looked for Lydia on 1841 and 1871 , she is Lyden in 1841 and Lelia in 1871. Her age in 1871 is shown as 75 , and born IOM.
On 1841 census she has children Elizabeth 3 ( BC Mar Qtr 1838) and Charles 1 ( June Qtr 1840).
Cannot seem to find a marriage for Thomas Heslop and Lydia.
So I just googled "Thomas Heslop married Lydia" and found a posting on this site in 2006 by Patricia Brown who names her Lydia Farrill ( Also Farril and Farrell). There is a reply from a Jackson Farrill in 2010 who gives her parents as Patrick Roche (also Roach and Rotch) Farrill and Elizabeth Lewthwaite.
Frances Coakley also replies giving a lot of detail on the family.
I still cannot find her birth, there are many sons and a Louisa ch 30/7/1802 who was "Privately Baptised" - as most of the children were - but this Louisa may have married 7/10/1830 St George, Everton, Lancashire.
Have you tried to get the BC's of Elizabeth and Charles to show mother's details ? Lydia's first daughter Elizabeth matches mothers name that Jackson Farrill gave.
Frances may be able to add some more detail.