Sounds like a form rejection. It means nothing except they didn't like the book enough to represent it. That makes no judgment on the quality of the book, it's just a no thanks. I got form rejections on a book that got me an agent and then sold. Everyone has their own tastes.
Generally, "a good fit" can be anything. They might represent, say, romance, but if all their romance clients are modern day light happy romance, and yours is a hot spicy dark romance, then you're not a good fit, even though it's still romance. Your book could be too similar to another client's, and there'd be competition for editors. Not a good fit. Everything they represent is third person distance narrator, you wrote a first person. Not a good fit. It could even be a nice way of saying "egads, this sucks. Go away." (though if she said she enjoyed reading the pages, I don't think this is the case here)
One rejection is nothing. I know it's hard, but you have to find a way to let this roll off you or you're going to make yourself crazy. Even when you're query is successful and you get multiple offers from agents, there will STILL be those who say no. Unless they tell your specifically what they didn't like, it's just "no thanks" and nothing more than that. The book can be 100% publishable quality and still get rejections. Think about all the books you pick up in the bookstore, read the back and set back down. That's a "not a good fit for me" rejection. You just weren't hooked enough to buy it.
You're ready when you feel like you're ready. Because here's the trick...YOU being ready means nothing. The BOOK has to be ready. And if it isn't and you are, you'll still get rejections. And you don't really know if it is ready or not. If you think it can be made better, it's not ready. (And I'm talking big edits, not tweak a words here and there edits) All you can do is make the book the best you feel it can be and send it out there.
A general rule of thumb is:
If you get no page requests from your query, it's either a bad query or an overdone idea. (usually a bad query.)
If you get pages requests, but no full requests, it's the pages. Either the writing isn't there yet, or the story isn't grabbing.
If you get full requests, but no offers, it's the book. The writing is there, but the story isn't grabbing.
After one rejection, you don't have a wide enough sampling to make any assumptions yet. Send out those dozen queries, see what happens, and then decide what to do (if you don't get an offer that is)