I'd ask.
When I married my wife (13 years ago) it was very chaotic, and we had someone else helping with the invitations. She wanted them done by a friend with very nice hand writing and I had a couple friends that didn't get invited. But being guys they said "hey what's up? I didn't get invited..." and that was fixed.

Could have been something simple like that, and she might be wondering why you didn't go to her wedding thinking you had been invited. Better to talk it out then keep wondering.