Is my mom entitled to everything that used to belong to my dad, including the money he asked me to keep in my bank account?

My dad recently passed without a will (in Las Vegas). Several years ago he gave me some money and asked me to keep it in my bank account (I live in NJ). My mom wasn’t aware of the money until a few weeks ago when I said I got it from dad and I’d use it for his medical care. Unfortunately my dad passed away too soon, and now my mom wants me to cut her a check with all the money, including interest. Is she really entitled to all of it? Apparently dad never told mom about the money. I’d do the same as mom is not trustworthy. I’d rather split it with my sister.