Nek0izTanK i believe she's worked for the company as long as she's been old enough to. she knew koko and her brother since they were children, possibly even since they were born. and she's been on again off again with the old man from koko's team. I'm not sure she had any story really before joining the company. probably just another top tier fighter in one of the world's militaries that was offered a job.
Chequita's such a badass! I would love to see what would happen if Chequita and Valmet ever went at it *shivers* just the thought of such an amazing sight makes me tingle all over ;) I assume that the whole world would be full of boners and wet panties if it ever happened lol