Complex sentence: Grubman is well known as a publicist for celebrities, founding her own company in 1996, and has represented Britney Spears, Jay-Z and the Backstreet Boys.
Split into simpler sentences: Grubman is well known as a publicist for celebrities. She founded her own company in 1996, and has represented Britney Spears, Jay-Z, and the Backstreet Boys.