She appears neither in the SAG register, nor in http://www.mytrees.com/ancestry/Other/Born-1878/Do/Doubell-family/C...
Sampie Kotze has her as a ongekoppelde
Sarah Anne Doubell * c. 1873 x Steytlerville 11.8.1890 Michael Henry MILES
Although I'm loathe to add a 17th child to Hesther Arabella's lifetime of pregnancy, her birthdate in 1873 does fit in an uncharacteristic gap of 8 years between children.
Sarah Ann Miles nee Doubell's Estate Papers; Depot: KAB; Source: MOOC; Vol. No.: 6/9/4417; Ref. No.: 41220
https://familysearch.org/ark:/61903/3:1:3Q9M-C91W-BSJZ?mode=g&i...
Names her parents as Walter and Esther, and that she was born c.1873 in Steytlerville