Depending on where she lives I would call the local county's extension office and ask if they have any 4-H groups for beginning sewers. That is the way I learned and now have taught many girls through 4-H. Nine is a perfect age to start.

This is the one I bought for my daughter, tho she is a bit older than Miss Nat. But it's good and covers all the basics of understanding a sewing machine and how it works. It's not "kiddy", but a good book for a smart, motivated 9 year old.
http://www.amazon.com/Me-Sewing-Mach...sewing+machine

It sounds to me that she needs to spend part of her Spring Break with her aunt learning how to sew.

There's a book out there called Kids Can Sew which I have used with children that age and I think is pretty good. You could also go to your regional Agricultural Office and pick up the 4H sewing book for beginners. They're usually pretty good.