honestly I quilt, and I can't help myself. I always have 3 or 4 that I am working on. I would probably send it to her, but why not put a note with it - - not necessarily a bill
Just sweetly say since your niece asked you to make it how could you refuse her?
The time and money put in the quilt - along with the love, makes this a priceless gift and that you hope she enjoys it. Its not a thing you would do for just anyone