Facial changes are due to fat, not bone. Most, if not all, of the fat in a person’s face will return to its former position after ceasing short-term testosterone just as body fat will (just like an MTF troon will have a softer features while on estrogen). The amount of time it takes to return to its former position will vary from person to person, and will depend on whether or not their hormones remain out of whack after ceasing (some people need help from an endocrinologist to get right again). “Past the point of any return to femininity” is pretty bold. Buck Angel is past that point. Grace is just a bearded lady on steroids who has terribly mutilated herself. For now.
(I only know about short term abuse though. Let me put it this way: I took great pains to not write the former post in a power level style, if you catch my drift. You would never, ever guess in a million years.)
ETA: Back on topic: Possible motivation as to why Grace would do this, and why it must drive Lena crazy: Lena doesn’t have the monopoly on big weird stories about sexuality anymore, isn’t the center of attention, and can never ever copy her without looking obvious and utterly insane. This is Grace asserting control. Lena is no longer is the person who did the weirdest and most abusive thing ever to Grace’s body: Grace is. How utterly fucking tragic.