Go to town to buy Christmas presents for Daddy and DD2, and having hot choc with Mummy.
Make potato stamp/handprint wrapping paper (DD 2 can participate in stamping or hand printing or feet printing!!).
Make a paper chain (using sellotape strips and a box of strips of different coloured papers so she can choose herself) for the hall or her bedroom.
Have a winter picnic in the sitting room watching a seasonal dvd with popcorn and hot choc/special cold drink (can of fizzy orange etc).
Go to local cinema.
Have a wintery walk, looking for signs of nature and maybe collecting pine cones.
(If you find pine cones, have a craft activity with those another day).
Bake cookies together. DD2 can stir things too. Give both the DDs a small bit of dough and rolling pin and cutters to enjoy - even if not all the results are cookable/edible.
Spend an hour (bearing in mind small people's capacity for such work, an hour is plenty) clearing out toy chest together and getting rid of broken toys.
Would your DD understand the concept yet of giving her a bit of money - say £10 - to buy a toy she might like but to give to a child her age who doesn't get presents? It also gives you a chance to find out what she's drawn to.
Make a card for nursery teacher. (And Grandparents, and Daddy, and little Sister, and Mammy.....)
Draw a Christmas picture to put in little Sister's bedroom.
Draw a Christmas picture to put in her own bedroom.
Draw a Christmas picture to put on Grandparent's fridges.
(You can also use free printable pictures to colour in if you like, there's loads on the internet. And some sites also have other activity pages like mazes, pattern and writing practice sheets, ideas for making decorations etc).
Go to see a local Live Crib (if there are any). Or visit local petting farm.
Learn a joke to tell Daddy.
Learn a Christmas song to sing to Daddy, and practice it singing to little Sister (while you can do something in another room or far side of the room - during awake but not food time, obviously, for DD2).
Read a Christmas story together.