Thanks for weighing in, everyone! I appreciate all of your ideas and I think it's a good suggestion to wait. But in my particular circumstance, if I were to wait it would have to be a whole month, and at that point I would feel no need to e-mail her since I'd be seeing her soon anyway. I could just give the letter to her in person. But I would feel like the "moment" had passed, whether that's valid or not. Do your views on the situation change since she has one more work day left tomorrow? She isn't technically on vacation yet. But yeah, I don't want to be panicking about this for so long...

I suppose I could call to ask if I could e-mail her, haha. But that would be a boundary thing too...