Your information re Sarah Hulme's second marriage to William Heywood concurs with what I have found, although I was not aware of William Heywood's previous marriage.
Do you have details of where James Hewitt died and where the record is located?
Also, do you have details of where Sarah Hulme was baptised?
Unfortunately the information that you have re the parents of Sarah Hulme does not tie in with what little information that I have. In the 1841 census for Hale, Ellen Hewitt and her siblings Mary, Hannah and John were living at Clay House with Hannah Hulme (aged 80) as well as a Sarah Hewitt who I believe was the product of an earlier marriage of James Hewitt. I have assumed that Hannah Hulme was the grandmother of Ellen Hewitt and that consequently Sarah Hulme's mother was named Hannah. I could of course be wrong which is why I posted my original message. If you have any ideas on who Hannah Hulme was, if not Ellen Hewitt's grandmother I'd be greatful for them.
I live in Timperley. Are you local to the area? How are you linked into the tree?