A big turning point was Teddy's death. Mia felt there was even less of a reason to keep fighting for her life. At this point Mia really wanted ti give up, but there was still Adam to think about, and other smaller reasons.
Before Teddy's death Mia didn't think much of her grandparents, but after Teddy passed away, she realized that it would be very hard for her grandparents to get through all of their deaths, which gave her one reason to try to live.
Mia still couldn't decide about if it was better to stay for Adam or not. It would be hard for him if she left but she felt that he would eventually get over it, but if she stayed then they would both go to different colleges and just be separated again.
Mia's condition had suddenly gotten significant't critical and she couldn't breathe. The doctors worked hard and took her to surgery to try to save her. This is a turning point because the reader assumes that Mia will die but when her condition gets worse we see Mia's reaction and we see that she gets upset, that she isn't ready to die yet.