Unique Security Deposit Situation

I'm a landlord in North NJ renting out to a tenant. She was moving out and put down a security deposit for her new home in NYC. A couple of weeks passed without incident. One day my tenant informs me that through no fault of her own, the lease for her new place fell through and that they need 30 days to return her security deposit. This affects her ability to pay me the rent since she's going to have to stay in the place I'm renting her. Can they do that, legally keep her security for 30 days when it fell through because of them? Is that standard practice and is there a way for me or her to get it back sooner? Thanks so much in advance!