Found a bit more (well, what else is there to do on such a cold, snowy and foggy morning!) ...
Having had a quick look at your PMT on Ancestry, I see that Ellen has a further sibling - brother William, who (according to the 1901 and 1911 censuses where he is recorded with his widowed father/siblings and brother-in-law Reuben respectively) was born in 1894 and died in the First World War.
Again, there doesn't seem to be any birth record for him on the GRO indexes.
However, this does at least confirm that their mother must have died between 1894 and the 1901 census. The most likely death on the FreeBMD indexes is for an Eliza TOWERTON (aged 37, ie. born c1859) in 1896 in Lambeth.
Checking out other Ancestry PMTs for TOWERTONs, I found one that confirmed (from a death certificate) that Eliza died on 15 FEB 1896 from complications following childbirth. The same tree showed that this Eliza was baptised "Eliza Ellen ATTRYDE" on 14 NOV 1858 at St. John the Evangelist, Clapham, Surrey, daughter of Charles Afred and Ann.
To be continued ... !