Understand that 'masochist' can imply emotional habits, not just physical pain. She's an emotional masochist, always dating people who treat her poorly.
Pro Tip 2/3
Not Only Sexual
Remember, it's not solely sexual; it can describe any self-inflicted suffering for gratification. Only a masochist would enjoy this level of workload with no extra pay.
Pro Tip 3/3
Negative Connotation
Be aware, calling someone a masochist can come off as an insult or criticism. Calling her a masochist for taking on the hardest projects wasn't a compliment.