The trouble with getting better is that it gets worse, before it gets better, Shezbut. I haven't even gotten to the part of therapy where we process the traumas I've experienced.
It is important to not do anything that you are not comfortable with. I know that is simple, but I have to still have to remind myself why I can't have a relationship with my family sometimes. If your gut tells you to not send the Christmas card, maybe that is the best way to go. If you have nightmares just thinking about them, what if they try to establish communication once they receive the card?!