Should I mention anything to my sister about NOT inviting a certain annoying person to join Xmas Dinner?

I visit my sisters about once a year on the holidays. Last year my middle sister invited an incredibly boorish, uninteresting woman who proceeded to DOMINATE the conversation effectively squelching communication at the table. My OTHER sister has invited this irritating person to Christmas dinner this year and I am oh-so tempted to say something, but since both of them consider this a friend - this friend has no place else to go for Christmas, I'm pretty sure that speaking up would backfire on me.