She's 78 so complicated games of strategy can be frustrating for her.
I played dominoes with my mother in her 80's before she died in the nursing home for MONTHS- she never got tired of playing- always wanting "just one more!" game. It was actually kind of fun, and we ignored some of the complicated rules in the instructions. We also livened it up with playing for dimes and playing 3 out of 5 game "championships".
Also, Parcheesi is a good simple board game that is easy to follow and has elements of strategy but also lots of luck of the dice.
You might want to put on some old Bing Crosby or other traditional holiday music she can relate to.