@Another2Cats thank you so much for taking the time to have a look.
Lily was born in 1898 and she's missing from the 1901 and 1911 censuses.
In 1901 I have Lily's mother and her five older sisters in West Ham, but no Lily.
I've tried looking for her with grandparents, but her paternal grandparents are another two who vanish from the records (and tbh I'm not 100% certain I have the right people - more of a strong possible).
Maternal grandmother was in Dublin and Lily wasn't there, nor with any of the aunts and uncles. Her father, Simon/Samuel is also missing in 1901, but he was a commercial traveller so probably away from home on census day. It seems really unlikely that he would have a 3 year old with him. Perhaps she was in hospital?
In 1908 their mother Maria is admitted to the workhouse with Violet and Matilda, but again no Lily.
In 1911 you have found Lily's sisters, Julia, Rachael and Violet (my g-grandmother) in Tottenham. The rest of the family are missing from the 1911 records, as far as I can tell. Their mother Maria lived until 1954, so she was definitely still alive. Adelaide (b 1893), Lily and Matilda (b 1903) are nowhere to be found in 1911, nor is their father Simon/Samuel (he was definitely alive in 1911 because I have him witnessing two of his daughters' marriages in 1916).
Would Lily be old enough to be in domestic service in 1911 when she would have been 13? Older sister Adelaide/Ada certainly could have been, and it's plausible because they were poor.
Lily married in 1922, so it would be worth my looking her up in the 1921 census I think.
Sorry for the massive essay, and thanks again for taking the trouble to do a search for me 