Sorry, I guess I've dealt with too many people who talk like that and AREN'T being sarcastic that I have a hard time telling anymore. Anytime I do use sarcasm online anymore, I generally overload it with emoticons to really get across the "I'm not serious" part.
Anyway!
I'm thinking my character is gonna be ex-military then, which would explain how she came to have the MEC suit in the first place. A really bad war injury, like a photon mine or something, basically horribly crippled her, so they wound up just amputating her ruined limbs, giving her the cybernetic hookups, and slapping her into a MEC suit for the remainder of the war.
After the war, she had to get by with the cut-rate military surplus prosthetics (aka defective rejects) to try to live a normal life. By that point though, she was military through and through, had spent long enough in a MEC suit that it felt natural to her, and was getting real sick of her crappy replacement limbs not working right.
So, one black-market refurbished MEC suit later, she wound up trying to get into mercenary work. I figure she met the crew while she was on a job (bonus points if it was at a production for one of the military manufacturing plants that made her reject prosthetics) and realized that she was really sick of playing rent-a -cop, so she wound up joining up with them. Sure, her current MEC suit is about two decades out of date and has gradually been repaired using everything from car parts to assembly line crane components, but it still works. Admittedly, she's the only one who understands HOW it works at this point and is the only one who has any hope of modifying / repairing it, but it works!
The scrapped together construction is also what prevents her from using ranged weapons like the military MECs do- the suit has absolutely no target assist systems and isn't a very stable firing platform. She could pull the trigger on a gun, sure, but she has no hope of really aiming it beyond 'face it in that general direction and hope for the best'.
If she ever were to get her hands on a proper, new, military MEC, she'd become a pretty devastating powerhouse for the pirates to use.