Mrs. Latham is the loyal secretary and bookkeeper for Cavendish Publications. In other words, she runs the place. Between Cavendish and Mrs. Latham, it's the Mrs. who's got all the math skills and common sense. The whole enterprise really should be called Mrs. Latham Publishers. We have no idea why she stays there. Even Cavendish admits he doesn't pay her well. Plus, her ten-year anniversary gift was purchased from "a British Museum Gift Shop bargain bin" (4.1.92). Oh, Timothy, you shouldn't have.
So why does Mrs. Latham stay on? Not only does she stay on, but she also saves the business when she catches the Hoggins brothers raiding the place via hidden camera. Is she just loyal to a fault or is she taking advantage of Cavendish's ignorance (he can't add two-plus-two without a calculator) and funneling money into her own pocket? It's something to think about.