Good for you and her mother for encouraging her to sew with REAL tools at a young age. I think using the toy stuff designed for children is just setting them up for failure. One thing I do to cut straight lines is mark the fabric on the edges where I want to cut then fold at the marks and press a crease. The crease makes it easy to follow the line. There are also gloves like this that are designed for cleaning fish.
http://www.cabelas.com/product/Cut-R...h-All+Products
The only problem is at 8 her hand would probably be way smaller than the glove.
Rodney