Already signed a contract but in danger of termination

My sister is working in a private school. She and her companions are required to undergo a two-month summer training before they can start teaching. She already trained for a month and was supposed to start teaching the next month. However, her two companions in their summer training were hired directly, she was the only one who was not yet hired even though all of them signed a contract. When I asked her about the contract, because she said they already signed it, she said that it was held by someone of high authority (I'll just call him A) and not yet notarized. And she doesn't have a copy.

She graduated in BSed. The contract states that she will be teaching in the high school division but she was later transferred to the pre-school division. She was then told by A that she should go home and that being a sales lady suits her more. A then told her that it was the admin's order to terminate her.

Is their move to dismiss my sister legal?