They should get rolling whenever you're ready to do the work, and hopefully she's willing and able to lead you along. Every sponsor takes a different approach, maybe she's waiting for you to ask as an indication of your willingness? Doesn't hurt to be reading the Big Book and praying on your own, the more the better IMO.
There's an AA pamphlet called Questions And Answers On Sponsorship that explains nicely the role of a sponsor. You should be able to pick one up at your meetings or read it online here
http://www.aa.org/en_pdfs/p-15_Q&AonSpon.pdf