What would you do if your cousin stole thousands of dollars from you?

Go to the police and have my cousin charged with theft.

First things first, don't ever tell or reveal vital information to relatives. Also, don't ever do business with them, it usually ends up being a disaster. If this were the mafia, cousin or not, he or she steals money from you, the cousin will end up in the bottom of the Hudson or Lake Tahoe.

Assault

Press charges 🤷🏻‍♀️

Report her to the police.

Confront her, kick her ass, and take all her nicd stuff she bought.