From the marriage entry (which I assume you have?), Lizzie's father was Robert.
So, 1871 census: Class: RG10; Piece: 380; Folio: 16; Page: 25
2 St James Street, Clerkenwell
Allen, Robert Head M 28 Packer b Lambeth
Allen, Maria Wife F 28 b Kingsland
Allen, Robert Son M 17 months b Middlesex
Allen, Lizzie Daughter F 3 b Middlesex