'It's okay,' I soothed, trying to fight back tears.
As a close-knit family, Amanda even got a job as a truck driver in the mines where our dad James, 58, worked. Then in December 2012, Amanda texted me at work to say she didn't feel well. I have a really bad headache, she wrote. I don't want to be here. I messaged back, telling her to go to the sick bay, and I went to visit her later that night. But she wasn't her usual, happy self.
'There's something in my head,' she kept saying. 'I need to get it out.' I was worried. Her forehead did look swollen. I rushed her to hospital and the doctors ran scans, but they all came back normal. So they gave her painkillers and sent us home.
But over the next few days, Amanda's agitated mood continued. Her boyfriend Nathan, 26, told me she'd barely slept and lashed out at everyone. Then, on Christmas Day, I woke to panicked messages from Dad saying Amanda had been admitted again.
Leaving the kids with their dad Carl, I rushed to hospital. But when I arrived, I had no idea just how bad things had become overnight. I soon learnt that Amanda had flown into a rage and tried to stab herself in the head with a kitchen knife, believing it would let out the pressure.
While Dad and Nathan desperately tried to restrain her, they had no choice but to call police and paramedics, who eventually sedated her. I couldn't believe what I was hearing. Amanda was a smart, sensible girl - what was happening to her?
When I was let into the ward, I wasn't prepared for what I saw. 'I want to go home,' Amanda screamed, rocking back and forth wildly in an attempt to free herself. It was like my sister was possessed.
A lumbar puncture revealed Amanda had encephalitis - a very rare inflammation of the brain caused by a virus. But as doctors tried to treat her, Amanda's condition deteriorated. She soon slipped into complete psychosis, refusing to eat or sleep.
When I tried to give her a drink, she spat it back at me and she hurled abuse at Nathan, Dad and the nurses. Transferred to the Mater Hospital's psychiatric ward, she was put under the guard of a nurse around the clock. We felt so helpless.
It was like my sister was possessed.
As days passed, Amanda's behaviour became more erratic. One moment she'd be screaming at me and attacking the staff. The next, she'd stare blankly into space. Things were so bad she reverted to acting like a child. One day, she turned on the bathroom tap and was splashing the water around like she was seeing it for the first time.
'Sissy, sissy,' she kept saying, like when we were children. The kids struggled to understand why they couldn't see their 'Aunty Manda'. 'She's very sick and needs time to get better,' I told them.
But I had no idea if the person they knew and loved would ever be coming back. Specialists were completely stumped as Amanda didn't respond to any treatments. If she ever got better, I knew she would never believe how strangely she'd acted, so I started making a video diary.
After a month, another specialist was called in. 'I want to run an ultrasound on Amanda's abdomen,' he said. I was confused. What did that have to do with what was going on in my sister's brain? But when the results came back, we were floored.
'We've found a teratoma on Amanda's right ovary,' the specialist informed us, saying it was a benign tumour made up of abnormal tissue, including brain matter. He said it confuses the immune system as it attacks normal brain tissue and the tumour at the same time.
'It's like there's a monster growing inside her,' a nurse said. Three days later, surgeons urgently operated to remove the 8cm tumour. Horrifyingly, it had hair and teeth. Amanda's case was so rare she was believed to be only one of seven people ever to be diagnosed with ovarian teratoma encephalitis.
I desperately hoped that after the operation Amanda would return to normal instantly. But she had a long road ahead of her. After a few weeks, she slowly started responding to us again. Dazed and confused, she asked endless questions.
'It's like there's a monster growing inside her,' a nurse said.
So I decided to make a storyboard with pictures of her family and friends to place at the end of her bed, so she was constantly reminded who she was and what happened to her. After another two months in hospital, she was finally discharged and started treatment with a brain-injury rehabilitation clinic. But she had no recollection of what she'd been through.
Incredibly, three months on, Amanda was feeling well enough to return to work. Given that we'd missed Christmas, we held it again in March so Amanda could open presents with her nieces and nephews. I felt so grateful to have my sister back.
Two years on, Amanda has thankfully returned to her old self and is doing really well. I'm so glad she was able to beat the monster inside her.
When Rachael showed me the videos of my behaviour, I was shocked. It was like watching a stranger. I felt terrible for how I treated everyone, but I don't remember a single thing from that time. I'll never be able to thank my family enough for not giving up on me.
Through everything, Dad never left my side and Nathan and Rachael were absolutely amazing. Nathan and I have now built our own house and I'm back at work. I'll have to be monitored for the rest of my life, but there's no sign that the teratoma will return.
I can't believe what I went through, but I feel so lucky to have my life back.
Originally published in that's life! Issue 10, 2015