Question about sending full manuscript

Meh, I'm of the opinion that resending looks unprofessional.

Resubmitting because you tweaked more does tend to send the wrong signal, like you weren't actually ready to submit. But this happens all the time. Unless you did some major changes, I'd probably leave it as is. Minor issues will be overlooked if the voice and story and writing is good. That's what agents are looking for first. If they don't love your voice, story or writing, then any minor changes you made probably wouldn't have made a difference anyway.

I wouldn't. Why would you want to tell an agent who requested a full manuscript that now another agent is going to have a 'better' copy? Good lord, don't even think about that.

If you didn't grant an exclusive to the first agent you have absolutely no obligation to let her know that another agent is considering your work. In fact, you can be assured that the first agent already assumes this to be the case.

And I would let the manuscript sit as is.