It really depends on how bad it is. It can last from a few weeks to years. And from years to decades. For such strong information, it's best to ask a doctor. The doctor can guess, but might not be right. But I hope you find care for her, and I hope she lives for a very long time! And I am very sorry she has cancer and I am very sorry the therapy is unsuccessful. :( Wish you and your girl friend the best!