Supergirl saved the school bus in "The Quest for Peace", 10 weeks ago, however the episode claimed 2 weeks later Lena called Andrea Rojas into her office to negotiate selling CatCo Worldwide Media. However, Lena had already sold the company in "The Quest for Peace", before Supergirl saved the school bus.
The flashback to when Lena and Andrea met each other takes place 15 years ago, although Lena is 26, which would mean she would have only been 11 then.