A commenter on this reddit thread seemed to know her name upon seeing the same photo and commented:
Maxwell pal, Tamara Mellon, Brit, OBE, co-founder of Jimmy Choo shoes and former/current sidepiece of ex-Disney President Michael Ovitz, who's still married to his wife. Rehab alumna.
Her wiki page:
Tamara Mellon, OBE (née Tamara Yeardye; born 7 July 1967) is a British fashion entrepreneur who was the co-founder of luxury footwear brand Jimmy Choo, and then the eponymous luxury footwear brand Tamara Mellon.
....
She is the daughter of Tom Yeardye, a stunt double for Rock Hudson, and Ann (Davis) Yeardye, a former Chanel model.
Ah, so Tamera is a child of two well connected, very good looking people. I can believe that.
She is English, so no kin to the Mellon Families of Pittsburgh, USA. They are worth over $12 Billion.