There are probably two major possibilities here.
1. She absolutely loves what she's read and wants to offer rep now.
2. She absolutely loves something about what she's read but has concerns about something else and wants to talk over possible revisions and see how open you are to "fixing" something she's concerned about before she commits to reading the rest.
Either way, it seems very likely that she's keen on your book and that's always a good thing.
There's a smaller possibility that she thinks the book is wonderful, but can't see how it would fit in her list and wants discuss changing it to a different genre/category, or she wants to encourage you to send it somewhere else where it would be a better fit.
As Oceansoul said, make sure you have your questions ready for her. I would split them into three groups - questions about her contract, previous sales, submission plan (for if she immediately offers rep); questions about her editorial/revision style, how much work she normally puts into a client's book before it goes on submission, if she asks for revisions what sort of time frame she expects from the author and what you might expect as far as her reading it a second time (for if she starts with wanting to know if you're willing to revise); questions about where she thinks the strengths of your book and writing are, what areas may need improvement, etc (for if she isn't offering rep or asking for revisions but is giving notes on what she read).
Naturally, if she is making an offer you want to talk about all three groups. If she's asking for revisions, you'll want to talk about the last two.
Congratulations and best of luck!
