I hadn't watched that video before, and I do like the quilt Jenny made. Such pretty fall colors!
She used only one jelly roll, and that was enough for 9 Dresdens, each of which went on a 22" square. If you figure out how many 22" (unfinished) squares you want for your quilt, that will tell you how many jelly rolls. For instance, if you use 16 squares in a 4x4 configuration and an 8" border, your quilt will measure 102" square, but if you use a 25 squares in a 5x5 configuration with the same border your quilt will be 123.5" square. Or you may want to use a bigger border or make a rectangular quilt or ...
Anyway, for 16 squares you would need only 2 jelly rolls, since one makes 9 squares, and for 25 squares you would need 3 jelly rolls.