If it is going to set you back then why go at all? What is important is your mental health! If you do have to go, don't really speak to her, just smile and nod and everything she says or if you feel you have to say something keep it down to small talk and just walk away if she starts any of her nonsense.

My ultimate advice is not to go but I also understand it isn't as easy as that especially around this time of year!