[JetMetFan]

How is there no such thing as straightening up within one's vertical plane? If she'd just been standing there all the time with her knees bent and then locked her knees while not going further forward than the front of her feet...

I know I've mentioned this before but a defender doesn't have to become a statue when establishing LGP. Here's the Verticality rule (I'm using the NCAA-W rule book since that's what's covered in the clip but it's the same for NFHS & NCAA):

NCAA-W 4-38
Art. 1. Verticality applies to a legal position. The basic components of the principle of verticality are:
a. Legal guarding position must be established and attained initially, and movement thereafter must be legal.
b. From such position, the defender may rise or jump vertically and occupy the space within her vertical plane.
c. The hands and arms of the defender may be raised within her vertical plane while the defender is on the playing court or in the air.
d. The defender shall not be penalized for leaving the playing court vertically or having her hands and arms extended within the vertical plane.
e. The offensive player, whether on the playing court or airborne, shall not “clear out” or cause contact that is not incidental.
f. The defender may not “belly up” or use the lower part of the body or arms to cause contact outside her vertical plane.
g. The player with the ball shall be given no more protection or consideration than the defender in the judging of which, if either, player has violated the principle of verticality.

According to these guidelines, what did the defender in this clip do wrong after establishing LGP? Section B allows for a defender to "rise...within her vertical plane." Presumably, a player's vertical plane ends at the front of his/her feet. Section F says the defender "may not 'belly up' or use the lower part of the body or arms to cause contact outside her vertical plane."