Spending time together is so important. Her mom's attention is all on Lore so the 11 year old may feel left out. So I think its important to spend time together with her.

I would definitely spend time on craft: making personalized Christmas cards, painting, I used to do charcol and pastel drawings around that age. And boy did I love to cook even back then. Took over my sister's Easy bake oven

If you don't want to make cookies from scratch, buy the mix in a bucket or even the ones in a tube from pilsbury. It could even be baking biscuits. Having hot biscuits you baked is a big treat for your niece. And crafts don't have to be just drawing or painting. It could be knitting, sewing. Make a simple pillow (case) with cute trim. Have her make one for her little sister. Or watch a movie together and share a bucket of pop corn.

And see if any neighbors have children her age and introduce her to them. When I stayed at my Aunt's house or my Uncle's house growing up, I used to play with kids in their neighborhood. My aunt would show me how to cook. and over at my Uncle's house, I used to draw, try to learn Calligraphy from him and went on nature walks.

If you are not sure ask your niece.

sicerely,
smilingcat