MIL was impossible during my wedding venue scouting trip. Am I overreacting to un-invite her from wedding-related plans?

My last post about my MIL got more traction than expected (here: https://www.reddit.com/r/inlaws/comments/1ogr62i/my\_sil\_bil\_travel\_for\_most\_major\_holidays\_my\_mil/) if you wanted some additional context of what I'm working with.

I am having a destination wedding in 6 weeks. Last week my fiancé, mom, and MIL all went to the wedding site (3hr plane ride away) to do a venue walkthrough, try the catering, and meet our other vendors. My mom really wanted to go, and we have no issues so I was happy to include her. I wanted to veto inviting MIL from the trip due to her being insufferable to travel with in the past. Fiancé insisted he could not leave her out as I am bringing my mom, so against my better judgement I agreed.

MIL was impossible on the trip, as we knew she would be. Anywhere we went, she was upset the menu wasn't in English. She had a hard time communicating with waitstaff because she refused to say even simple phrases in their language, and she would get frustrated with them (and visibly show her annoyance which was extremely uncomfortable). I suggested she brush up on common phrases or let us order for her, and she had the nerve to snap at me and say "I will keep speaking MY own language, thank you very much!". I responded in a very gentle tone "just a reminder, we are in their country" and she freaked out and said she will do as she pleases.

10 minutes later she goes back to acting chummy as if nothing happened. The whiplash had a really lasting effect on me and I didn't speak with her the remainder of the day. I'm really sensitive to arguments, my heart races and I have a hard time re-regulating my nervous system again- it really fucks up my energy. This is common: she will often lash out in a very harsh way, and then act like it never happened. My fiancé iced her out too and did not speak with her, but I genuinely don't think she understands what she did wrong. If he were to correct her she will escalate further, so we just have to ignore her.

There were about half a dozen other instances like this where she will freak out. Before our catering tasting, my fiancé and I were running late (coming from my hair/makeup trial in traffic) and she had the nerve to call him and say 'fuck this' and 'fuck that' and she is not feeling well, she'll just skip it and go back to the AirBnB, whatever. We get there and she's perfectly fine. But my fiancé was a bit shaken and we all had to do a 180 to enjoy the tasting.

The issue: I am not getting married in the country my wedding is in, it is easier to do the paperwork in the US so we are getting married at a courthouse in about 4 weeks, and are having our symbolic wedding in March. We planned for our parents and my fiancé's grandparents to join us for that and a lunch after, as his grandparents are not in good health and cannot go to our March wedding.

I told my fiancé that based on MIL's behavior and nastiness towards the both of us, I want to omit her from the courthouse wedding. He said we cannot do this, and I said he needs to choose me over her. He agreed and said he will omit her, but if possible he wants to talk to her first and have her apologize to both of us. Basically if she apologizes, then she can come.

She is a vibe ruiner everywhere she goes, and I don't think she's capable of having fun or not centering a day around her. At the venue walkthrough she had an 'allergy attack' because of a scent they had at the venue... the focus is ALWAYS on her and I want ONE day where it's about me and my fiancé. Even if she apologizes, I kind of want to leave her out of the courthouse day anyway as a precaution. What would you do in this situation?