An employee in The Sausage Factory, the Mechanicsburg coffee shop. She's only on stage briefly, but plays an important role in convincing Herr von Mekkhan that Agatha is a real Heterodyne. When Agatha goes on her and enters the madness place, she starts giving caffeine-wired orders to everyone in sight, to help her amass the stuff she needs to repair and improve Vanamonde's coffee engine. Not unreasonably, this requires getting her hands on coffee beans, since they are required for making coffee, after all.
Rinja gets ready to smack Agatha around a bit -- which we gather (from Van) is very much her normal mode of operation -- however, it doesn't take her long to succumb to Agatha's Sparky charisma. In moments, she's with the program and Agatha is on to the next convert, Herr Mitrant. What matters is that Agatha gets her coffee beans, her chance to build something new, and a following. Van and his grandfather are impressed by this whole affair and start down the path of believing that Agatha may really be the Heterodyne heiress she claims to be. (As Krosp puts it in so many words, well, duh.)