soo why can't she be a badass female knight if her true skils are that great she could try to be acepted as a girl. what is the point of her acting average and pretending to be a boy. She is keeping the same surname so it's not like they don't know about her family background.
It's a really bad exuse just so they could put a crossdress trope in there.
Also if she just wants to be a average nobody how does the crown prince's"Do you want to live as Estella instead of Estien?"offer from the description work? wouldn't that be... ooohw I don't know.... Drawing a loooot of atention to her.