I have a long list of activities that many are for smaller DCs but can be modified.
So going for a nice walk in the woods is still a good idea, for brisk fresh air and to look at nature changing - just maybe not gathering pine cones to paint anymore.
Perhaps not exactly a duvet fort picnic, but an afternoon curled up with hot choc and festive DVDs together could be nice.
I would still play Christmas music while doing my preps - but maybe get more into classical, jazz, country options instead of just Children's songs. (Try Live365 internet radio, there are about 20+ festive channels to choose from in lots of different types).
Does your DD like cooking at all? Would she like to be responsible for an aspect of the family celebrations? Maybe Christmas Eve dinner, Christmas morning breakfast, or the bread sauce, or trifle, or....insert family favourite or new idea here... Also, take the chance to start teaching her the kitchen skills over the quiet time, and some family recipes to pass on.
Volunteering is great. Whether the buying something for someone in need (see last post) or helping out somewhere. Or maybe something like bringing some baking to the local Fire station or police station for the people who look after us all year. Local pre-schools/nursery may welcome an extra pair of hands for an afternoon in the run up.
At 12, she may be gone beyond "crafting", but might love the idea of an afternoon getting messy with glitter and paint together. Or give her the bits with a friend to make cards or whatever. Perhaps a few more "grown up craft" bits in the materials would be useful - so glass painting, or being allowed at the sewing machine to make a tree decoration, or acrylic paints instead of just poster paints.
While you are cooking dinner one afternoon, she might like to sit at the table and stuff cloves into oranges and just chat. But give it as an option- (and you can do it later if she's not interested, so still having something nice for decoration and smell).
In the quiet days afterwards, have a few things planned. Again, thinking of her interests - can you arrange a meet up with a friend of hers over the weekend or before NYE? Will you be doing any visiting to wider family? (Are there any visits that she will start to find boring - so can she bring a good book, or can she stay at home, for some of those?). Will you be going to the sales, particularly will there be an opportunity to go together (and can she get a half hour or hour by herself in that trip)? Or is she responsible enough to leave at home while you go?
Are there board games she likes to have a family night? Card games? Get in the crisps, nice drinks, and set it up together. You may even want to get a new board game - there are lots that are more "grown up" and range from activity to thinking to just silliness. Find one or more to suit your family.
Sorry for the length of my posts - I probably have x-posted with most by now, I just got started and kept typing.
But enjoy. And don't put too much pressure on either yourself, or the rest of the family, to have a magical time. Just try to have a nice time, and if there is magic, so much the better.