There are times when it makes sense to revise after you've submitted, such as when you have received a Revise and Resubmit that you want to do or have received feedback from your subs that resonates with you. I wouldn't mess with a partial, but it's possible that a full request might be worth contacting about...maybe. I never have, despite some R&R situations. When I might: 1) if an agent rejected me and told me they were rejecting for the exact things I revised, I'd mentioned that I already revised it; 2) maaaaaybe if I was doing a status query at the appropriate timeframe and the revisions were already done. In the case that I would mention it, I would say that the changes were due to agent feedback (which would be true in that case). If she asks for a full and you made significant changes to the novel in between, I'd mention that then too.
This agent probably saw your leading paragraphs when you queried (most ask for a sample), and possibly has already seen them by now in your partial. It's not likely she's going to reject after asking for material based on that. It sounds like you just polished it, instead of making significant changes, so I wouldn't worry about it. If you get rejected and no reason is given, then just let it go.
