If she put down a deposit to hold the unit, then as long as she came to take by the date she was suppposed to, they cannot give it away. If they did, she can sue them to force them to give her another unit and/or to give her compensation in addition to returning her deposit. She would be well-advised to retain a landlord-tenant attorney to help her.But if she did not come to take possession of the unit in time and missed the date she should have moved in by, then they could re-rent it to someone else and would be entitled to keep the deposit due to her breach (not taking possession when she was supposed to).