My (25F) MIL (60F) wants everyone to take a lie detector test because someone gave her dog food at her Christmas party

My MIL Linda always throws a Christmas party every year at her house. She invites all her friends, children, their spouses and grandchildren.

This year it went normal and we all had fun. The next day Linda’s dog Princess wasn’t feeling well and unfortunately passed away at the vet. They determined she had eaten something she shouldn’t have and my MIL is convinced one of us gave her something. She now demands everyone take a lie detector test or else the next Christmas party will be cancelled. She’s distraught and is accusing people of murdering her dog.

I’m going to be blunt and say Linda wasn’t a good dog owner. Princess wasn’t trained properly and had many emotional issues. Linda was also notorious for giving princess food she shouldn’t eat and we’re all convinced she made princess sick by accident.

Nobody wants to pay for or take a lie detector test so what are some other ways we can help her grieve? Also how can we convince her that her idea is ridiculous?