Edith's birth may have been either:
Edith Gertrude SMITH Q2 1909 Woolwich 1d/1234 or
Edith Maud A SMITH Q2 1909 Woolwich 1d/1260.
Or maybe it wasn't either of these: in the 1911 census, Florence said she'd been married less than a year and had no children from her marriage to Walter Smith. But that might mean that Walter was the father but the birth took place before he married Florence, whose first husband (John Thomas TUSTIN) had died in Q3 1909. It's even possible that Edith was John Tustin's child but not registered as TUSTIN.