Agent response question: R&R or more? Or less? What to do next?

I shouldn’t still a querying newbie, but this silly question proves I totally am. I’d love the advice of some seasoned query junkies and agented writers.

A few weeks after a full request, I received a response from the agent. After a few brief paragraphs about what she loved and thought could be improved, she hit with the main thrust of the letter—she thought it would sell better if I switched genres. If I wanted to consider those changes, she’d love to talk about it further. If not, she’d love to see my next book.

Switching genres isn’t a minor decision, so I spent a week working out basic plots changes and tried to figure how many major revisions I’d need. (I had some major research to do.) I needed to figure out if this felt right for me, and I decided it was worth a try. It’s all a learning experience, right? I grew excited. I emailed the agent back saying that I had several ideas, and I’d love to hear what she had in mind.

That was three weeks ago. ::cue crickets chirping::

So, is this just a revise and resend? She wrote that she’d like to “discuss it further.” We're talking massive changes—I’d hate to redo the whole thing when she was thinking something else entirely. I'd REALLY like to discuss what she has in mind, since she has proven her ability to sell works like mine–and like what mine could become. I don’t want to seem pushy or high maintenance though.

Since it’s been three weeks, should I assume that she’s not going to respond? Assume the email was lost in the black hole of her inbox and send her another email? Nudge her? Is this normal, or is she just busy? Just rewrite the whole thing and send as an R&R?

Any suggestions, oh wise ones?

She wrote three paragraphs about what she loved about the ms and a few suggestions to make it stronger. Then she described how the ms straddled two genres, and how she thinks it would sell better as one over the other. Then from paragraph four: "I thought this was a great read, but I think that I would have trouble selling it in the ________ market. If you are interested in considering some changes to the book in order to gear it more for the _______ market I would be happy to talk with you about that further. Otherwise, I would be happy to look at future submissions if you care to send me something."

I wrote back that I'd be very interested in hearing about what changes she had in mind—if she even got the email.

I know she's taken on several authors who wrote their ms in one genre, then sold it in another (with major revisions).