She has vivid memories of the day she fell ill and her battle to fight back to full fitness.
Like many others who have suffered viral meningitis, Petra's symptoms started with a headache which grew progressively worse. A school friend had stayed over at her house the night before and after Petra walked her back to the Tube she felt weak, so weak she had to return home by taxi.
She told the Daily Mail: "My legs felt like lead and my handbag felt as if it weighed a ton – I was so weak I thought I was going to collapse."
Taking her temperature
Back home Petra's mother Slavica took her daughter's temperature and called a doctor. The GP arrived and advised that the ailing teenager needed hospital treatment, and that she might have meningitis.
With Petra feeling worse and worse and her mother in tears it was left to father Bernie to drive them to hospital. Once admitted Petra was given a lumbar puncture, an experience she will never forget.
"It hurt like hell," said Petra. "I vomited after the puncture, but thankfully after that I was given anti-nausea drugs. The doctors put me on a drip too, because I was becoming dehydrated."
The lumbar puncture showed that Petra had viral meningitis and she was told she had to stay in hospital. She said: "When I found out I’d be staying I was so scared – the thought of one night alone was terrifying. And because the doctors were concerned at my rapid decline, I was convinced I was going to die."
Bed-bound for weeks
After she returned home from hospital Petra was bed-bound for three weeks, she lost nearly a stone in weight and struggled with her concentration and energy levels for months afterwards.
A month later she was back at school but had lost nearly a stone in weight. She says she was far from well when she returned to her studies – she remained too weak to play sports and found it incredibly hard to concentrate in classes because she felt so tired.
"Before getting meningitis, I was such a hypochondriac, worrying about the slightest ache. Ironically, I overlooked meningitis because the symptoms seemed like flu. I guess you don’t realise how healthy you are until it is taken away from you".
Meningitis scared the hell out of me," said Petra. "I realise how important it is to look after your health, especially your immune system. I still take lots of supplements and regularly have acupuncture. I do still have a tendency to Google any bizarre symptoms I might have. But I try to focus this energy into raising awareness about meningitis.
"It is essential people are diagnosed quickly, regardless of what type they have – if I’d ignored my symptoms I might not be here today."