Is the $500 a typo? I would consider $50 to be extremely generous from an aunt. For my coming-of-age day many years ago, the biggest single cash gift I received was a mammoth $100 from one of my grandparents, most other relatives gave in the range of $10-20. The most expensive in total was a ~$400 bike from my dad since mine had been stolen a few months prior. I still use that bike, almost 14 years down the road.
But then again, I felt insanely happy with my ~$500 total in cash gifts from that day. Then I got to school the next day to learn that one of my friends had received $5k worth of funds invested by her parents. I nearly fell off my chair. And that was only one gift, so there are for sure different norms for different families. I think it would depend on how much you know her. She might receive a lot of jewelry from parents and grandparents already. Is there a way you could put some of it in a fund that she can keep track of? That way she could see her money grow bit by bit, which could be a nice, practical lesson.