The phone call -- maybe

What makes you think it's only considering representation, rather than a call to offer rep or ask for an R&R? I've never heard about an agent calling just to feel out an author. Obviously, if you and she don't mesh on the phone when she calls to offer (or ask for an R&R), either of you can say no, but if the agent is calling, they're pretty serious about your book.

I have had an R&R via phone call, so it does happen, but I think it's pretty rare compared to phone calls that are offers of rep. If it is an R&R, you can't really know what she'll ask for until she does, so just be open to considering anything she asks, and don't be afraid to get at the root of where a suggestion is coming from, and if a suggestion doesn't work for you, discuss other ways to deal with the underlying problem she's seeing.

However, unless something in her e-mail made you think there's no offer coming, I would prepare to ask the offer questions (which include some similar things to R&R, if you ask about revisions), and take anything else as it comes. Remember that you're feeling her out. Be prepared to ask questions that will let you know if she's the right fit for you.

I've certainly seen enough "I don't know if she's calling to offer or to ask for an R&R" posts (from folks similarly unwilling to commit to believing it's an offer) to know that agents often neglect to mention it. And most of the time, it is an offer, not something else.

I don't think you're 100% wrong about the feeling you out part, because part of their reason for talking instead of e-mailing is to get a sense of you, so that they can say, "Never mind," but I haven't heard of an agent backing out of an offer unless the author was wildly offensive.

Fingers crossed!