It appears to be a Baskerville, but I don't know who's...

It's always been Baskerville - but can't confirm whose either...
Some people on this board have worked on her identity - maybe they'll chime in.

http://www.typophile.com/search/?keys=kate%20spade

Good Lord. Thanks guys. I did the Kate Spade search on What the Font and didn't think to do it here.