California is an-at will employment state. What this means is any employee can quit and any employer can let go without cause as long as it isn't against the law (which is insanely difficult to prove to begin with). Any offer they provide to her (salary, earn out, etc)... Would not have mattered if they hired her on and let her go a day later... Ultimately contracts are fickle like that. There are probably exceptions to all of the above but most likely difficult to enforce in the end.

This is the sort of thing a founders agreement should cover off. Relying on "hey, we're all friends" doesn't cut it once the corporate lawyers get involved.

Have you never worked a job in which you've never wished some people to get fucked over?