More than a few times she considered her options before she knelt in front of the Dark Lord alongside her former best friend. They were not Marked early on in their captivity. They were not given the impossible choice to become a Death Eater or die. Only the Dark Lord's most loyal and faithful followers were allowed to have the physical proof of their devotion permanently etched on their left forearms. To be gifted with the Dark Mark, they had to earn it. At any point in her training, she could've refused. Antonin even tried to talk her out of it several times. He wanted her to understand the sacrifice that she was making, to know that there was no turning back.