This is from a bride's perspective ...
My DH and I wanted a small wedding, and laboured over our guest list. We didn't want to cause offence, but found ourselves making hard decisions.
We ended up inviting some of our friends' partners/spouses, but not all. We made decisions based on how much we liked each partner, whether we'd been invited to their weddings, whether they would have childcare issues, etc. It was really hard for the most part.
Some of my friends' partners weren't invited, and a couple of them msgd me to ask if it would actually be ok if their partners came too. Each time I was surprised - there's no way I'd ever ask that, I'd just enjoy it on my own - but was quite pleased that the partner might have wanted to enjoy our day too. Each time, DH and I said absolutely, bring them along!
... every one who did that in the end didn't even come. I was devastated. One had a newborn and another couldn't afford it, so that's just life. But another friend didn't even return the rsvp and didn't make contact - haven't bothered seeing her since. Another, my BFF from high school, I msgd 2 days before to ask her something else about the wedding arrangements and she said 'oh nah, I won't be coming after all'. She claimed that she and her DP had broken up and that she was keeping a low profile. I was pretty heartbroken. Didn't help that she was evidently not keeping a low profile at all. Never heard from her since.
My point is that you don't know your bride's reasoning and you were more focussed on taking offence than on trying to understand, that you two seem to have communication issues otherwise your (plural) communications would have been more open and direct, that sure she might not have been perfect but neither have you, and that - if this person really is your friend - it would be a huge waste to allow this to affect your friendship.
My other comment is you haven't mentioned how your DP feels about this. Does he care, and if not why are you letting it get to you? If so, is he contributing to your feelings or in some way choosing to encourage you to feel isolated rather than excited for a fun time away from your regular life?
Sorry for the length of the post! 