Missy seems surprised by the idea that you can use information against someone as a form of revenge. However, Missy was the one who taught Sheldon to use the fact that his opponent for school president wasn't a native Texan against her in season one.
When Sheldon has his epiphany about zero, he quickly consults Dr Linkletter in his office at the university. It is well-established the university is in a different city than the Cooper home in Medford, and Sheldon needs to be driven there daily. However, all the Coopers that could drive Sheldon are seen back in Medford while he's with Linkletter. Plus, when Sheldon returns to continue his tutoring session with Billy, it seems like little to no time has passed.