At this age – unlike when she is older – Baby won’t wake up early on Christmas morning. Let her sleep to her usual time, despite any temptation to wake her up because you’re so excited. The day will be tiring for her, so it’s best for her to have as much sleep as possible before the festivities begin.
As far as possible, let Baby keep to her usual nap time, as well. Ask the host for a quiet room. Over-tiredness leads to irritability and tears. She’ll have a much more delightful day if she’s well-rested.