Lisa might have a point, here. If the agent says she'll work the contract if you get an offer, that kind of limits the types of publishers available to a non-agented author--not all of them, certainly. Likewise, if she is not getting any significant or advances at all from her effort, it means that she might be subsisting on royalties only.
I'm all for a agent stepping up to the plate and deviating from protocol with the desire to help authors. Has she mentioned about subbing your book to any of the significant publishers? By unsolicited interest, does this mean she contacted you first? Kind of an out-of-the-blue thing?
Remember:
1. Experience--does this agent have contacts and inroads into the larger publishers who furnish competitive or industry standard advances?
2. Longevity--how long has this agent been in business? This item reverts back to #1
3. Knowledge Base--Does this agent know literary contract law inside and out?
4. Compatibility--is this agent easy to work with and does she specialize in one or more genres, which includes your books or stories?
5. Track Record--this goes back to experience, but roughly how many book sales and how large is her stable?
6. Agreement--is this an agent to writer contract offer or is this a (non-paper) handshake agreement? (Not too much of a problem either way here, but if you sign with her for two years and want out, you'll need to find out about that provision.
I'm just saying proceed with caution. Personally, I would be leery of this until time tells and the results are in. Just saying.