In 1871, Sarah Ann, age 15, is in service unfortunately.
There isn't a Sarah Ann Edwards born or living Warmington on the 1861 census. However there's only one Edwards family and they have a 4 year old daughter Mary Ann. I can't see this Mary Ann on later censuses, nor can I see a birth registration for her. Maybe, if someone has access to christenings, they will be able to confirm or disprove that she's the girl we are looking for:
1861
RG9/963 136 9
Warmington, Northamptonshire
John Edwards, head, 27, Ag lab, b. Lincs Morton
Mary Ann, wife, 27, b. Warmington
Mary Ann, dau, 4, scholar, b. do.
Elizabeth, dau, 2, b. do.
William, son, 1, b. do.