I think you should calmly ask her about it, in person. Just imagine if, say, your invitation had been lost in the post and SHE thought YOU were rude for not responding. Or imagine if it was a particular organiser who doesn't like you arranged it and told the bride you hadn't responded, when she actually didn't invite you. Or maybe the bride had it mistakenly in her mind that you were away or already busy on that weekend, and so didn't invite you. Or maybe the bride thinks you hate parties, or something.
My point is, just imagine if there was an explanation and you lose this friendship over it. Think what a pity that would be.
And if you ask her about it in person, you can guage her body language.
I think it's absolutely crazy to let a close friendship go after something like this, which could be a complete misunderstanding. You can be perfectly nice about it, and it will either clear the air, or you'll come away knowing that the friendship is over, if she gives you a load of old codswallop. If it's the latter, you can easily nod along and say "Oh yes, I thought there must be an explanation" so as not to give her the satisfaction of seeing you hurt, IF her intentions turn out to be bad.
I'm in my fifties and I can tell you that old friendships are precious once you are older. I think it would be a terrible shame to let this one go without communicating with her. You have been good friends for a long time, and people who knew you when you were young are dear, and become more so as the people around you die. At least honour that friendship with the clear communication it deserves before walking away without a clue what happened.