My take was that Kazumi (tomboy) started working at the civil engineering business of Nachi's family (thus her hauling boxes around in front of trucks, like the trucks we see on page 2.) Meanwhile Nachi might have taken the hostess job for some income until the theater starts doing better. Which it hasn't ("skin of my teeth") but isn't dead yet either.
Basically they were forced to work, but swapped the jobs pressed onto them, which is a more appropriate configuration (tomboy Kazumi works with trucks, dress-up Nachi works with men.)
Also they became closer... somehow? Weak link, there.
Also, the math confuses me. They're 4 years apart, but Nachi has graduated from college, while Kazumi is considering dropping out of high school. Isn't college in Japan 4 years? Or did Nachi do the equivalent of an associates (2 year)? But the sign said "womens university", sounds like the full deal.