I've first heard the phrase on QI (season 3 episode 6) where Stephen Fry uses it as rhyming slang for "buzz"
Stephen: "Woman who does": buzz.
Stephen [laughing]: It's all I could think of!
Phill: Oh, oh. So we're doing middle-class Cockney rhyming slang!
I couldn't find it anywhere and wrote it off. But then I heard it again used in the White's Blues by Fascinating Aida. Sadly I couldn't find the lyrics but it seems to refer to a nurse that takes care of the singers infant. The song can be found here.
Am I right in assuming the phrase refers to some sort of housekeeper duties? Also does anyone have any idea where the phrase originates or where it is used? I've never heard it before but it seems to (according to Phill's comment) be tied to (presumably British) middle class society.