Mother in law has bowel cancer

Mother in law had op 8wks ago, consultant has said it was worse than he first thought and couldn't remove all of the tumour, we were told 12 weeks then fastrack at the moment she seems fairly well but can't grasp that she will deteriorate and it maybe quick how quick could it be ? We are concerned and would like a time scale but she's not being honest with us when she sees the doctor.