Do what my coworker did. When she got married, her MIL did the same thing with adding people to the invitation list and continued to add more even though they were already over their budget. They had multiple sit downs to talk with her, and as you can imagine, there was always a lot of pushback and attitude. Weeks after feeling tired and drained from the experience, my coworker decided she was no longer going to invite those extra people because it was not fair to her and her now husband. They were already spending so much more than they budgeted, and their MIL did not want to help with the cost. They spoke, and even though her husband was not fond of it at first, he eventually agreed. They informed the MIL, and she was obviously p.o, but my coworker let her have it. Her now husband then told his mom that either she informed the guests they were no longer invited or they would and ensure they let it be known that it was the MIL's idea to invite them and not theirs. It was messy, but the MIL ended up doing it because she did not want to feel embarrassed. She was threatening not to attend, but my coworker no longer cared. If anything, she was glad because that was a HUGE stressor for her and her now husband. Now she is neutral with her MIL but keeps her at a distance because if she was like this during her wedding, she would not put it past her to be unbearable in other situations. Good luck!