How legally binding is a text message?

Question Details:

My friend was going to move into an apartment at college. She had agreed with the other people she was going to move in with that as long as no illegal drugs were used she would be the third person to move in. Yesterday she caught them using an illegal substance and does not want to move in. There has been no lease agreement signed or any physical paper signed to agree on moving in. They say that they have a text message stating that she would move in and that they are going to sue.  Do they have a case? And if so, what would her losses be?

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