For every would-be criminal mastermind, there are a dozen failed attempts, and Rosie is one of them. The way she tells it, she had her villain identity all picked out, complete with a costume and a catchy name. Alas, "the Riveter" had a less than riveting debut, most likely because she is not the greatest planner (as she freely admits).
In the end, it was easier to just hire out her services as bodyguard and strongman to other, more ambitious criminals. Over the years, she worked for more than a dozen different bosses, and she is the source of many of your contacts in the criminal underground.
It's a dangerous world out there for a woman, something you found out once you started looking for a way into the Enhanced underground in Derana's body. Apparently, you were deemed a suspicious presence, and people decided to ask you a few "questions" in a dark alley on your way home.
Rosie took offense to this, and once the dust had settled on the bruised bodies of your would-be assailants, you made sure to buy her a drink. It turned out that she had shelved her villain career as the Riveter. She now hires out as muscle to other, more ambitious criminals.
It is Derana that knows and interacts with Rosie, and as far as she knows, the two of them share the same, mysterious boss.