This is going to sound wild, but bear with me: invite her by name. Take the high road, seriously. It's small potatoes on your big day and you'll be so busy you probably won't notice her there. Plus, no concrete evidence you don't want her there means you're not the bad guy.

If you think she's going to show up and pull a stunt, you can have a bridesmaid/best friend keep an eye on her and tactfully redirect her, keeping a buffer between you guys all night. A guest in a white dress is annoying but everyone who knows you will know who the bride is.

There are a lot of ways you lose by explicitly excluding your friend's long-term partner. If you really can't have her there, either don't invite your friend, or only invite your friend and heavily restrict plus-ones. Or gamble and hope he doesn't pick her. The only way you lose by inviting her is maybe seeing her in passing, or through momentary discomfort of her embarrassing herself.

In any case, good luck - it's a very sucky situation. I'm interested to see what other people say!