Where to buy fine jewelry in SF

It’s my sister’s 40th birthday in October and I want to get her a nice piece pair of earrings or a ring in the $500-$1000 range.

I don’t want to buy from Tiffany or Cartier as I feel like half the cost is the brand which no one will see.

She had a rough divorce and hates that all her “good jewelry” is from her ex.

Where should I go? reputable and fair?

Vintage/antique is cool as is new.

Thank you in advance!