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The 20-year-old flew to Auckland last Thursday for a scan which showed a ''big'' stress fracture in the navicular bone in her left foot.
She had had problems with the foot since January.
It reached crisis point at the world championships.
She was forced to withdraw from the 100m and 200m after barely being able to walk following her 200m heat on the first day.
The Paralympic gold medallist went on to finish fourth in the long jump with a distance of 5.21m - 1cm off bronze and 6cm off gold.
After investigating various possible causes for the pain, it was a relief to finally have an answer.
However, given the pain had subsided for now, the diagnosis came as a surprise.
''Finding out that I had a stress fracture was a big shock. It was a huge shock to be honest,'' she said.
''I don't think anyone thought that was what was going to be wrong, considering I don't have any pain now.
''I guess you think back and you put the pieces of the puzzle together and you're like 'wow, classic, why didn't I pick up that that felt like a stress fracture then, or it felt terrible then, or why did I do that?'
She faces a lengthy rehabilitation period, having to keep off her foot for six to eight weeks, before beginning to build back her strength.
While unsure of the exact timeframe, she said six months had been mentioned as a possibility should things progress well.
Having been born without a right hand, Grimaldi was unable to use crutches, but had a frame to rest her leg in, which helped her walk.
Aside from ducking out to classes for her quantity surveying diploma at the Otago Polytechnic, she was spending most of her time relaxing at home.
While hard to look back on, she was proud of her performance at the world championships - as she says ''fourth by 1cm isn't too bad with a broken foot''.
Despite that, it was not something she was keen to go through again.
''It was an interesting campaign and one I probably wouldn't want to re-live, ever.
''It was just so mentally tough knowing there was something wrong with my foot, but not knowing exactly what it was and trying to figure it out, but just having no luck.
''And trying to push my body to do things that I knew it could do and it could do two weeks ago, two days ago, and all of a sudden it couldn't do it.''
She would not rush her recovery, knowing there were two years until the next world championships.
Being back fully fit for the 2020 Tokyo Paralympics was her major target.