Furtiveness isn’t your best play. For one thing, the agent will probably recognize the project. I know agents and editors who can’t remember what they ate for dinner last night but who can remember details page-and-paragraph from a story they read years ago. That describes me, in fact. There’s a reason folks like myself choose this profession. For another thing, most agents will take a second look if the project is indeed different in a big way. Just explain in your new query letter that you’ve substantially reworked the story and then let her make the call. That’s professional, respectable, and commonplace. The agent in question was interested enough to request sample pages last time, so clearly the concept intrigues her. I predict she’ll say yes to the second look.