What role did Mary Kate Olsen play in Ledger's life? Was she dating him?

I just read an article that says the housekeeper called Mary Kate several times before calling 911. Was Mary Kate dating him? Sorry to ask this, but I hadn't seen anything in the Aussie magazines about a romance or anything about the two of them. What relationship did they have? Does anyone know. I am sorry for his family, his former girlfriend and daughter and for Mary Kate too.