She has a rare condition called Addison's disease that means instead of producing adrenalin to deal with stress, her body shuts down her vital organs.
It means she started revising for her AS Levels months in advance after the stress of her GCSEs left her in hospital following a major attack last summer.
Jennifer, from Prestwich, Greater Manchester, said: "The illness leaves me very tired, so my mum often finds me asleep in my books while I've been studying.
"I know I can't let myself get unnecessarily stressed out, so I have to be much more organised than my friends.
"As a result I have a strict schedule where, if I do an hour of revision, I have to rest for two hours before doing any more. So I start preparing weeks in advance of everyone else to fit everything in."
Jennifer has also been forced to turn down interviews for Oxbridge because she fears the stress of studying away from home.
She added: "I have been offered the chance to go and view Oxford and Cambridge Universities as part of my college's Gifted and Talented students programme, which is such an honour - but I just don't feel ready to move away yet.
"My college has been incredibly supportive - my teachers know the danger signs and can call my mum straight away if they think I'm getting ill."
Jennifer, who is studying geography, psychology, business and photography, hopes to become a child psychologist but fears she would have to sit too many exams.
She added: "I want to be a child psychologist, but it's hard to study for exams because they're really stressful.
"I did most of my revision last year hooked up to a drip in hospital - my weight dropped to 5st 10lb because my stomach stopped absorbing fats.
"I was thrilled when I managed to gain 10 A grades and 2 A*s though - all the stress paid off!"
Jennifer was diagnosed 10 years ago after eating salt straight from the shaker during a family holiday.
Her mum Amanda, 51, said: "In many ways it was a relief to finally know what was wrong, but the condition is hard for us all to live with."