YTA - your wife getting an invite as a guest and not a bridesmaid is not in any way equivalent to not inviting her at all. Its your wedding and you can do as you like but escalating like this is surely going to damage your relationship with your brother.

my fiancée has tried to forgive and forget, but it’s still uneasy between us because of the singular lens we now know she views my fiancée through.

That's a pretty big stretch, excluding people based on their looks from a photo OP doesn't mean they don't see any other value in that person.

FYI buying matching bridesmaid dresses that aren't too expensive and also 'suit' the body types of a variety of bridesmaids is usually one of the most stressful and argumentative parts of wedding preparation. This isn't a minor issue and if your SO isn't close to your brother's wife she wasn't obligated to go through that.