Landlord Lied About How Many Tenants, Left After 1 Day, Refuses To Return Security Deposit

Posting for a friend. She lives in Los Angeles. She found a room for rent on Hot Pads. She spoke to the landlord on the phone and he said it was only him. When she moved in she found out he had a daughter and 2 dogs that was not disclosed. The next day someone walked in the house and she was confused. He said he was the new tenant. Turns out there was another tenant who rented a room before her. So 2 tenants, the landlord, 2 dogs, and his daughter none of which was disclosed and was told she was the only renter and the landlord. She asked how turn the heat on and he said there’s no heat and said she should buy a space heater. She packed up her stuff and left. She asked for the security deposit back of 1000 dollars and he said ok. Now he refuses to give it to her. What can she do to get that money back? Any official legal sources she can send him to show what he did is illegal? Thanks.