I am sorry for your family's loss. It is hard to loose those that you love. I come from a big family and have seen a lot of passing in my time.
Maybe you could take her to a local nursery and let her pick out a tree, talk about what her uncle liked and what he would have chosen himself. Then let her plant it in a special place that she can go to it when ever she is missing him. Her own special place that she can talk to him or just remember the times they had together. Maybe taking care of the tree could be in some way, like taking care of him.
A couple of years ago my nephew passed, his cub scout troop planted a tree at the little leauge field where he played and now his younger brother plays at that field and it is comforting to him to have his brother's tree there.
I know nothing is ever going to take the hurt completely away, but hopefully this will help in some little way.
Kimberly