Ah, OP, I really feel for you. I live in a similar situation (Brits overseas) and it's happened to me, too.
Now, I don't know the situation, or the woman involved. But here's the thing: some expats are still living in secondary school. They are trying, for reasons best known only to themselves, to divide and conquer, and to appear more popular by making other people feel unpopular. I don't know if that's what's going on here, but I have seen it a few times. Some people move overseas, lose contact with friends and family, and then seem to unhinge a bit and start doing rubbish like inviting everyone on the street... with one exception.
Here's what I'd do: DON'T avoid the subject. If the night out is mentioned in front of you, simply say, I wasn't invited. Freely admit to all who will listen that you're feeling gutted about it. You don't need to go on about it, but don't cover up your hurt and disappointment.
Because other people will start telling your THEIR stories, either about that very woman not inviting them to something, or about similar things happening to them. People will sympathise. Trust me, it has happened to them, too!
Then, if you'd like to, throw a party. And invite that horrid woman along with everyone else on the street.