According to the Criminal Register she was born in 1887 in London and there is a baptism which may be her
Dora Martha Sadler
Baptism 26 Sep 1887 St Pancras, Camden
Father George Sadler
Mother Mary Jane Sadler
There is a few trees on Anc that list this Dora Martha Sadler if you have access
https://www.ancestry.co.uk/family-tree/person/tree/5019123/person/66830982/facts Her father is listed as George Christopher Sadler b 1860 St Pancras and his wife Mary Jane Halpin b 1865 Marylebone who was the daughther of James Halphin and Dorothea Sparling which might be where the middle name of Sparling originated
Kay
Added - Newspaper report Dundee Courier 5 February 1924 Report on an appeal re the case reports a letter from a man named Halpins who said that Sadler's mother was his sister which ties in with the info I posted above