I'd say the math and her grasp of how to use it to solve a problem like this was far more impressive (especially for a then sophomore in HS) than any actual folding that may have occurred.
I worked it out this afternoon, and its not too terribly difficult to get a nice closed form solution (as opposed to a recursive (or iterative one). Its mostly a bit of geometry with some cleverness moving things around to get a nice closed form solution. The only advanced math is a geometric series that comes up at the end, which gives the final fully closed form solution for the length of the paper given a thickness, initial length, and the number of folds. It becomes easy then to solve for an initial length for a number of desired folds.
The fact that she was in high school when she did this though, is impressive. Any teacher with a bit of calculus would have been able to guide her though, once he saw where she was headed.
