Some questions
You mentioned Elizabeth's siblings, whose details per parents agree with what's on Elizabeth (and Jane McReynolds) death cert- do you have their names and dates of the siblings, and which documents name their parents? Also, is Elizabeth documented anywhere as the sister of Hugh and of Jane?
I see Jane Mooney married James McReynolds in Ireland, in the Townland of Drumgarner, Derry - it gave her residence as Glebe (which comes under the Kilrea Parish):
1865 MARRIAGE : 12 Nov 1865 , Drumagarner, Derry, Ireland
James McReynolds X 24, Bachelor, of Drumlane (father James McReynolds Farmer)
Jane Mooney X 24, Spinster, of Glebe, (father James Mooney Farmer) to James McReynolds
Witness: Charles McGrath, Nancy Keenan
I see Elizabeth in the Census after marriage
1881 CENSUS: At Blackwoods Land High Woodlands, New Kilpatrick
William Butler 36, b Ireland (abt 1845)
Wife: Elizabeth Butler 35, b Ireland (abt 1846)
Son: John Butler 11, b Milngavie ( 1870, he is son of Jane McAllister, William's first wife)
1891 CENSUS: At 54 Kirk Street, Milngavie
William Butler 47, Labourer, b Ireland (abt 1841), Mason's Labourer
Wife: Elizabeth Butler 45, b Ireland (abt 1846)
Son: John Butler 21, b Milngavie (abt 1870)
Boarder: John Butler 20, b Ireland
Boarder: James Campbell, 60 b Ireland
1901 CENSUS: At 54 Kirk Street, Milngavie
William Butler 60, Labourer, b Ireland (abt 1841)
Wife: Elizabeth Butler 53, b Ireland (abt 1848)
And I see William Butler in 1871 Census on Kirk Row, with his son, in the household of McAllister in-laws. Do you have Elizabeth in 1871 Census?
Cheers
AMBLY