Hello Alexlisa, a warm welcome to the forums.
cPTSD is a complex PTSD, not that I'm a doctor to be able to say, however, is there a possibility that your parents have decided to try and put it behind them because if any of it is brought out to the open, then they and/or you might react in a negative way.
Xmas time can be difficult for many people where families decide to air their differences, especially when alcohol is involved, but you are entitled to either see them for a few moments only or make up an excuse to avoid them.
Sometimes it's better to mention why you can't see them beforehand, rather than the actual day when they're straight in front of you.
If you can I'd be direct with your psychologist and tell them that this current problem simply isn't going away and are they able to address it another way.
You have to look after yourself, and what happens if you're wearing a blue coloured dress that you like but your mother doesn't, then the same situation would arise.
Take care.
Geoff.