If the child has any inclination at all, you will probably not have to worry about attention span. A few rules, some consideration with breaks, even a little variety are easy enough to make a workable relationship.
Considering that most eleven year olds I have known in my life pretty much had living figured out (as far as their desire to participate,) ten years old is plenty old enough to teach the girl enough to make her a life time quilter.
I am currently working with a highschooler on her senior project. She was attempting knitting - - I introduced her to loom knitting, and she has surpassed my abilities or desires ... loom knitting is one of those activities that takes about five minutes to learn and a lifetime to master.
When I was oriented to the factory, they had us sew along lines on paper, just to get used to the machine movement, learn controls, and accuracy. Since that is how I start all of my teaching with any newbie, I accidentally stumbled on to something that actually taught my student quarter inch seams, which she produced eight half square triangles at the same time.
I do not have the program, but my friend prints out "Triangulations" for our half-square triangle projects. The way the lines are drawn, helps a student understand the seam allowance concept, while following the dotted line -- it actually revolutionized my student's sewing.
Perhaps someone can show you a link for how to make your own grids