”How does she justify that?
After reading that a half dozen times it looks that is the author's wish (whose picture makes it look like she could lose a few pounds) and not the 5'3" woman who wants to be a Marine officer. Someone who was 5'3" with the proper weight of someone 6'3" would not be described as "petite".
We have overweight women describing themselves as "curvy". I respond "Victoria's Secret models are curvy. YOU are just fat."