Thank you for your new question and for asking for me to assist you again.
If your sister has a signed contract, your sister can now bind the person to the lease. This means your sister can sue the tenant in court to force the tenant to pay damages for their breaching the lease and also attorney's fees for their intentional breach of the lease. Unfortunately, your sister does have to sue to get her recourse, since it is obvious this person has no intent to honor the contract she signed. When your sister wins a judgment against the tenant, she can then seek to garnish the tenant's wages from her employer and also can seek to seize any of the tenant's bank accounts to satisfy the judgment from the court.
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