I'm using logic. Since Newt and Rick were terminated because they were running for president in order to prevent a conflict of interest, it would leave Fox News open for wrongful termination lawsuits if Fox News allows Sarah to continue to work while she runs for president. Also, the executives at Fox News suddently met with Sarah after she started her bus tour, an event that looked suspiciously like a campaign event. After the meeting, Fox News said that they were not changing her status. If Sarah did not assure them that it was not part of a presidential campaign, they would have needed to suspend her just as they suspended the others.
But I find it interesting that the people that defend Sarah as the most ethical person in the race rush to defend her on technicalities. If Sarah knows that she is running, she has a moral and ethical obligation to tell Fox News - to continue to accept a paycheck, while knowing she would not be eligible if she was truthful about her intentions, would be dishonest and unethical, even if it might be technically legal. I thought Sarah was supposed to be above such technicalities...