I have, in theory, the requisite three LoR writers. Two of them are great and have long since uploaded letters for me into Interfolio. The one who supervised my undergraduate senior thesis, though, who knows my work best, hasn't responded to my emails since last spring. But she was on leave last year, and teaches on the quarter system where classes only started ten days ago. So I waited until fall, emailed her once in September and once last week with SoP drafts and application status updates--extra news so as not to seem nagging as I tried to reinstate contact and get that letter out of her. I've emailed the secretary of the undergraduate section of her department, who says that this third recommender is back in town, in the office, and will "hopefully" get back to me soon.
No one else is in any good position to write me a letter. Does anyone have any advice to navigate this without appearing horribly naggy and out of line? I want my letter, or at the very least, affirmation that it will come by the deadline.