I don't know if this will help but just wanted to note a couple of things-
Maud is baptised 31 Aug 1879 St. John, Hackney, William's occupation is clerk.
I don't know how much the trees have looked at William so I looked for just William Watson Willis and a marriage in 1872 to a Mary Ann Pittock has his occupation as Mercantile Clerk.
Maud's baptism address is Queen Ann's Road whilst William Watson Willis in the directories and electoral roll covering Maud's birth and to 1885 has an address of 146 or 186 Finborough Road (Kensington and Chelsea)
His probate record 1900 has an address of 146 Finborough Road, occ accountant, widow Mary Ann Willis.
I don't know if he is Maud's father so noting this just in case it helps in anyway.