Back to your original question
I've known agents who wanted to see if clients could shape a book to their liking before offering representation.
Your original question, I believe, was one of ethics: What if someone offers you representation in the meantime.
You certainly have no binding obligation to the agent who is offering suggestions--just as she has none to you.
As a matter of courtesy, were I in your situation, if I were offered representation by another agent, I would at least want to call up Agent 1 and tell her the offer was on the table and see if she wanted to get serious.
On the other hand, if the agent of your dreams offers representation, then you probably owe it to yourself to simply write Agent 1 a nice e-mail thanking her for all her input and time...and then sign with Agent 2.
PS. The average divorce rate seems to be about the same, too.
Keep in mind that you should be as courteous as possible, but this is a business decision. The rules of, say, dating ettiquette, don't apply. Signing with an agent is a marriage.