OP - I’d never post on MN about something like this in a million years, but presumably you started this thread to seek opinions and see what a variety of people thought?
Although - it doesn’t seem like it, because you’re getting very annoyed by anyone not encouraging you to feel hurt and excluded.
I don’t see how it is helpful for people to do that.
I don’t think your friend has necessarily done anything wrong.
Obviously none of us know exactly what has gone down.
But my take on it is - one of her friends organised this and invited people, and she doesn’t think it’s OK for her to then add other people in.
It isn’t a matter of just asking - ‘it is OK if I invite X?’ I don’t always feel OK asking this, because (as a sensitive person myself), I worry that the person I’m asking will feel obliged to say ‘yes’, even if they don’t particularly want to. So I don’t ask in the first place.
This isn’t about you - and I mean that in a kind way.
Your friend’s group has organised something, and your friend doesn’t want to upset the equilibrium. Nothing to do with you, per se.
She knows there will be plenty of other opportunities to socialise with you, and the group as well, in the future.
I’m just trying to encourage you to not feel excluded and hurt by this, as I genuinely don’t think you have any reason to.
But if you’d prefer only to listen to people encouraging you to think your friend acted in bad faith, by all means, ignore my post.