Aunt recently became her financial guardian, so she may be claiming that your grandmother was making poor financial decisions and saying that she was being taken advantage of. She'd love to shame you into giving back the money from the sale of the car, but I don't see that she has much of a leg to stand on here legally.
So go forward, be nice to your grandmother, (don't stop visiting her now that she's given you the presents)and see if Auntie can follow up on her threats. Elder financial abuse isn't just receiving one or two big presents from someone who could afford to give them, it would be more likely that she might show a pattern of your coming around and asking Grandma for money, and not coming around when you weren't going to be given anything or threatening not to visit if she didn't give you something.