Katie Milby, 13, has Morquio A, a degenerative syndrome which affects about 105 people in the UK.
It leads to the progressive deterioration of mobility, health and stamina.
Her friend Kyle Pirrie has started a petition seeking to see the medicine Vimizim made available on the NHS.
There is no known cure to Morquio syndrome but the drug improves the life of people with the condition.
It replaces a missing enzyme which allows children to continue to grow, as well as improving stamina and the ability to walk. It also relieves pain.
The drug's manufacturers have been providing the treatment to patients at their own expense but they are going to withdraw it unless the NHS in England and Scotland commit to funding it.
The Stranraer Academy student said her life would be markedly different without the drug.
"I wouldn't be able to move I'd just be in so much pain," she said.
"And I probably wouldn't be able to go to school."
It was that situation which prompted her friend to launch the petition which now has nearly 2,000 signatures.
"As a friend I suppose I felt kind of bad that she was going to be denied this because I know she has got a great outlook on life," Kyle explained.
"She's funny, she's friendly and I would hate to see her in pain all the time."
Galloway and West Dumfries MSP Alex Fergusson has also backed the petition.
"This is not a cheap medication but, as Katie herself asked me, how do you put a value on a human life?" he asked.
"There are only just over a hundred sufferers throughout the UK, with just five in Scotland, and those who have had treatment with Vimizim report a massive reduction in pain and the other symptoms of this syndrome.
"Life expectancy, which rarely exceeds the mid 20s without treatment, can be considerably extended with this treatment, and it is enormously to the credit of Katie and her friends that they have raised this petition to try to ensure that the treatment is available to all."
The Scottish Medicines Consortium said the drug was currently going through its assessment process.
It added that a decision on the medicine was expected to be published in early September.
A Stranraer Academy student has set up a petition to ensure a life-enhancing drug is made available to a fellow pupil with an extremely rare disease.