By the age of 12 to 18 months, your toddler can now understand more and is generally capable to find out what is going on around her. Around this time, she can already communicate her thoughts to you and so it shouldn’t be hard to understand what she wants (mostly). Although your child is still young to fully understand the concept of Christmas, she can already take part in various family traditions.
If you are planning to take her out and see Santa Claus, make sure to explain to her how he looks like through pictures. Do not force your child to have her picture taken with Santa if she does not want to. Remember that there will be lots of other chances for her to see this jolly fat fellow who is wearing a red suit in the coming years.
You may also go out and drive in your neighbourhood to watch the sparkling of Christmas lights in each house. Baking cakes and giving them out to your neighbours can be a good tradition to start with her. This can also be a good chance for her to start learning the essence of giving and sharing her blessing to those who are in need.