I really like the theory behind Jenny's videos but they sometimes lack in execution. This is one of those blocks.
The problem is that Jenny is trying to make HSTs (half square triangles) in the first step, but she is actually cutting pieces for QSTs (quarter square triangles) and then sewing them into HSTs. This is no small difference because it means that every piece you are working with after the first step has only bias edges. This leads to a lot of stretching and distortion even if you are very careful.
In theory if you start out with the same size squares from a single layer cake your blocks would all end up the same size. In practice they don't because as you are cutting and sewing and then recutting and sewing they will be distorted differently.
I made a sample block using Jenny's method. After the first step the four squares were about 6 3/4". I trimmed them to 6 1/2" square to give myself a better shot at a good block. After the second step (sewing the four squares together into a four patch) the block measured 12 1/2". I made my cuts for the third step at 2 1/16" from the center of the block. After sewing the block together into the nine patch it measured 11 5/8" more or less. Even with being incredibly careful, making sure I was pressing and not ironing, it's still wonky.
I do appreciate what Jenny is trying to do - bring quilting to the masses and make it easy enough that a beginner can finish a quilt in a reasonable amount of time. I'm just not sure that teaching bad fundamentals to beginners or other quilters is a great idea. I would have been frustrated if I hadn't learned the difference between making HSTs and QSTs, and ended up with a wonky quilt as a result. Quilting quickly is not always quilting well.
Off my soapbox and back to putting together my progressive learning BOW program.
Here's my block: