Have you seen the original baptism image and does it indicate an age?
I looked at the baptism records on familysearch (no images, only index). On the same day as Florence Gertrude was baptised there was a Ernest Gill, son of Samuel and Sarah, baptised. This may well be the boy registered in March quarter of 1876 with mother's name Lomas; there seems to be a marriage in 1874 (
https://www.freebmd.org.uk/cgi/search.pl ) that matches. The week before they'd had an Edith Mary Gill also baptised - she was born in 1874.
Sadly, both of the Gill children seem to have died around the same period, Edith Mary in late 1876 and Ernest in early 1877. It is possible that Sarah also died - there is a woman aged 30 by the name of Sarah Gill who died in 1877. The illness of the younger children might have spurred a family otherwise a bit lax with baptisms to head to church.
If these records line up (and I would suggest at least the 1874 marriage record to doublecheck), then in 1877 she was most likely either back in the hands of her mother's family (perhaps took the name of an uncle who married one of her mother's sisters), or went into care.
