Help my dad (50sM) is bringing his new wife (40sF) to the family gathering

I?m on mobile sorry for formatting. This kinda urgent,I need advice as soon as possible as they are literally on the way rn
tl;dr my dad is bringing his new wife (affair partner/ home wrecker) to the family function without telling me in advance.I haven?t seen her since she broke up our family 10 years ago and idk what to say to her.
Important backstory, way back in 2011 I was 11 and had a best friend, ?Liz?, we were inseparable. Soon enough, our parents became good friends too, the four of them would all hang out and talk while Liz and I played. Fast forward to a random day in summer of 2012 I wake up to my mother absolutely hysterical, literally SCREAMING at the top of her lungs. Turns out Liz?s mom, ?Mary?, had just called my mom to let her know that my dad and her had been having an affair behind everyone?s back. All those times where my mom and dad and Liz?s mom and dad were hanging out as 2 couples, Mary and my dad had been secretly fooling around.
**** really hit the fan after that. My mom had several mental breakdowns (turns out she had undiagnosed bipolar). She honestly blamed me partially for the affair happening because they all met because of me and my friendship with Liz. My dad left and didn?t come back. Mary?s husband kicked her out, divorced her and kept the kids. I never spoke to Liz ever again.
A couple months later my mom randomly ran into Mary on the street, words were exchanged and Mary slapped my mom in the face leading to a physical altercation, Mary was arrested.
Shortly after this incident my mom packed up our stuff and we left the country. I never got to say goodbye to anyone.
My mom and I moved to America while my dad stayed overseas, we had very little communication over the years but in late 2021 my dad confessed to me that him and Mary had actually gotten married after alll that. Apparently they are really happy together. He talks about her better than he has ever spoken about my mom.
Fast forward to right now, all of our family is gathered for a funeral and my dad is flying in, another family member let it slip that my dad is bringing his wife,Mary with him. I guess everyone knew except me. They?ll be here any minute now and I really don?t know what to say to her. On the one hand I?m happy that my dad is happy but on the other hand it?s super messed up how they got together, also my mom has consistently referred to Mary as ?the b*tch that ruined our lives? and I know for a fact that if I speak to her my mom will take it as an ultimate betrayal.


Source.