@mahtan I was wondering the same, so I went back to check; we, the reader, got an explanation of how the consuming works in chapter 12, after they met Benno the first time, but no one bothered telling her. She discovered the name by chance talking with Frida in chapter 20, but she didn't get an actual explanation, even after the big crisis.
I would like to point, however, the "slavery" contract can't be as bad as they depict it; that is, IF (and that is a really big if) you can find someone willing to do that.
Standing what we are told, her father, the leader of the gate guards, earn about one small gold coin in a year. If someone is willing to invest at least ten times that, he will treasure you, if only to get his investment back. The biggest problem is to prove that you are worth that kind of money, but once you do, you are most likely to keep doing what you are worthy for, maybe with even better funding. In Myne case, inventing new products (or maybe teaching advanced calculus, that would be really groundbreaking)