Re. What was the basis for thinking her (Selina's) father was Eli - did this come from the 1915 marriage details?
No, The 1901 census lists Eli Gillen Head b1861, Mary A Gillen Wife b 1867, Selina E Gillen Daughter b 1891, Frances E Gillen Daughter b1892, Lilian K Gillen Daughter 1897.
The same census has no entries in Kingston for a Selina Gillian or Gilliam.
Yes the date of Eli death (1918) is correct, it also appears on his army record. Being a reservist, he was reconscripted for WW1, but taken off the troopship because of ill health, which doctors thought was TB. He died in 1918 after 2 years of hospitalisation.
Roy G