The film, which is based on the book of the same name by Jodi Picoult, features Cameron Diaz as a mum who has another child to be a genetic match to her older daughter who has leukaemia.
Alex, from Kent, had been suffering fatigue, numerous headaches, her stomach had swollen and she noticed bruises appearing all over her body.
She had originally put her symptoms down to being 'a lazy teen', and didn't tell anyone because she was worried about "making a fuss".
But she then saw the film, recognised her symptoms and saw a specialist. She was diagnosed with chronic myeloid leukaemia (CML) three days later and immediately began a gruelling course of chemotherapy.
She is now in remission after two years of taking the powerful chemotherapy drug Distaniv - and her condition is now manageable.
"It was one of those surreal moments in life," says Alex. "I was watching the film and all of a sudden I realised I had the same symptoms. It was terrifying at first but I started to rationalise it and thought - I can't really be suffering from cancer.
"But I eventually went to my doctor and he sent for blood test straight away. When I was first told about the cancer, I was in shock. I thought it was the end. I just thought I am going to lose all my hair and just keep getting more and more ill.
I suppose if it wasn't for the film I may not have got my diagnosis in time. When you watch something on screen it makes everything much more real.
"I guess I am just really lucky to have watched it. However, I can't bring myself to see it again it is too upsetting - I have hidden it under my bed."
Alex went to see her doctor three weeks after watching the film. Medics found she had a white blood cell count of 490,000 while the average is just 4,000 and immediately diagnosed her with leukaemia.
But she was told her chances of survival were much higher, thanks to spotting it early. Left untreated her health would have rapidly deteriorated and she could have died in less than a year.
Only 600 people a year are diagnosed with CML and it is extremely rare in teenagers and children - particularly in girls.
Alex, who lives with her dad Ben, 41, a carpenter, step mum Em, 39, a freelance photographer, and younger brother Toby, six, is currently in her first year of A-levels studying English, Maths, Art and Psychology. She is hoping to go on to study at Cambridge.
Emma is now fund raising for the Royal Marsden Hospital with her friend Nancy Devine, 14, who also suffers from cancer.
She says she is determined not to let the past slow her down: "I just try to get on with my life - there is no point on dwelling on the cancer or wallowing in pity. I can now go out with my friends and do the things a normal teenager does."
Good luck with rest of your recovery Alex!