I hope that either I'm misreading Julie's silence and this ends up being a non-issue, or it blows over in time, but even if it turns out she is upset and stays upset, I don't particularly feel the need to "make amends". It is my and my DF's party, and we get to choose the guest list. I shouldn't have to apologize for or feel guilty about that.
Julie is the only guest that there is any question about regarding attendance, so there would be no need to "double-check" with anyone else. Among our family there has been frequent, open communication. 7 of our 12 guests are flying, and have forwarded their flight itineraries with passenger manifests, 2 of the 4 driving guests were in contact just last night, and while I haven't spoken to the remaining 2 drivers for about 2 weeks, we discussed their plans when last we talked and I am confident nothing changed.
Also, so long as we don't go over occupancy, the exact head count really doesn't matter. We're not having a seated ceremony, we're catering everything ourself and the number of servings are far from an exact science, and we have enough of everything that were putting in our favor bags that I'll just make one for Julie too in case she does make it.
I could push Julie for a definite response as to her intentions, but right now it just doesn't seem worth putting any more energy into worrying about, particularly if she doesn't seem to care to talk right now. In short, I'm letting go of the drama of will she show or won't she, because the answer has no bearing on last minute preparations, and right now I'm more concerned about last minute preparations. (It turns out that figuring out a shopping list for a full day of menus for 15 people is a lot more complicated than it sounds. And it sounds fairly complicated.) If Julie chooses not to come, I will miss her, but it is not going to devastate me, or ruin our special day. If Julie chooses to bring a plus-one after her request to do so being declined, I will be disappointed that our right to choose our guest list was disrespected, and I'm not going to let that ruin our special day either.