It's possible that I'm way off base here, and I haven't gone back to re-read this thread in detail, but I'm kind of wondering if Julia thought she was doing the right thing by not showing up for the wedding?
I say this based on the following thoughts: the OP said (IIRC) that she and Julia were close, but could go long periods of time without communicating. Julia maybe spoke without thinking when she said that she wanted to be at the wedding, but the OP did invite her, which was a very nice gesture. Maybe Julia didn't realize just how small the wedding was, and so when she asked to bring a guest, didn't realize that it wasn't a trivial question. And maybe at that point it all clicked, that the wedding was very small, that it was family only, and that she was never actually on the original guest list. So maybe at that point, or a little later, Julia decided that it would be better to simply not attend?
Obviously, if that was the case, she should have communicated this to the OP, given some explanation, etc. Unfortunately, we've seen often enough on this board that many people don't observe these social niceties. Particularly if they're the least bit awkward.
Not that I'm trying to defend Julia, per se. Just wondering about alternative explanations for her failure to attend.