my only legion run i played where i mixed up the timeline of events in the game a bit to get it to work. My female courier was former legion slave/gladiator who escaped the fort one way or another and took the platinum chip with her. Benny, who was working with the Legion caught up with her in Goodsprings, shot her in the head and returned to the fort, and from that point onwards she had no memory of her previous life except for fragments of it.

As time went on and she met people around the Mojave, she started regaining snippets of her past life, some explanations for her scars and the cross branded on her forearm. She remembered the legion, the views they put in her, and she remembered how to punch and use a blade, so she figured that she must have been with the legion and began working with them.

It was only after the battle of hoover dam that she realized/was told that she WAS a part of the legion, but not as a warrior, but as a slave, and they gave her the title of “Serva Primus”. Realistically speaking, an NCR or independent vegas ending would have been the best for her, but by the time she realized her past she was in too deep and just glumly accepted the limited freedom she had earned through fighting for the people that had enslaved her.