Ellen gave her name as Ellen and age 17 in an 1857 census when she was living with James Sr, Jr. and Rachel (Rankin) McCormick as a weaver. However she married as Ann Livingston. Her father was listed as a laborer.
A William and Ann Levison baptized Ann Jane in June 14, 1840 at Knocknamuckley. Possibly they are weaver William and Ann Livingston of Clare who had William John baptized Feb 19, 1843, but they had dau Ann Jane bapt July 28,1844, so that seems unlikely.
I have heard Elizabeth Thompson was your William's wife, but they were married in 1821, so there should be many more earlier children. They may be the couple in Ballydougan having son James baptized May 25, 1836. He may be the servant living in Ballygargin in 1857 at the home of John and Fanny (Black) Reid. If so, it sounds as if the Levingston family broke up due to deaths perhaps in the 1850's.
A marriage to Ann White occurs August 19, 1841 after the baptism, so that seems unlikely. Levingston/Livingston has been well researched, but there are few Williams.
Here are other Knocknamuckley entries:
1848 10 August David to William Bess Levison Moyraverty
1842 11 December William James to William Eliza Levison Bleary
1845 25 July Margaret to William Elizabeth Levison Ballydougan
1852 26 October Elizabeth William and Mary Ann Levison ,Ballydougan
1853 23 January Robert William Henry and Ann Levison Ballydougan
Seagoe record William and Ann had Sarah Jan 9, 1850 (I did not get the location)