Just tell her Marxism was written by some upper-class man-child who had the bright idea that you could run a country like a family. Which means you have to care about the other people involved, in order for it to be fair, and how many people care if somebody they don’t know gets fucked over?

That’s why it’ll never work as a system of government: human nature. If it’s any consolation that’s also why libertarianism will never work either.