But the day after finding out Martyn was one of the victims, the teenager bravely sat down to take some of her General Certificate of Secondary Education (GCSE) exams, a set of tests high school students in England and Wales take every two years. And despite the horrific circumstances, she absolutely aced them.
Nikita's older brother, Dan, shared the news in a Twitter thread on Thursday, which has since gone viral. He said Nikita's school told her she didn't need to take the tests because it was possible to calculate her predicted grades without them.
But the teenager insisted, and ended up getting eleven A* grades, the highest mark a student can get. In his tweets, Dan calls Nikita a hero and the "toughest person" he's ever met.
"Under the most horrific conditions, after going through (and continuing to go through) it all, she didn't skip a beat," Dan wrote.
He added, "I have never been more proud or amazed by anyone."
Like Dan, people on Twitter were floored by Nikita's resilience in the face of such a devastating loss. Users called her "a force of nature," "incredible," and "inspirational."
But the teenager was much more coy about her achievements, telling BuzzFeed News that taking her exams helped her cope with Martyn's death.
"I'm good at school — it's the one thing I have. So right after, when there were loads of people at home, I could get out of the house and focus on something else," Nikita said. "The house was full of people the whole time, so in a weird way it was nice to sit [for] an exam, have something to focus on. And school is my thing."
Nikita got top grades in the following subjects: math, further math, biology, chemistry, physics, geography, English language, English literature, French, music, and classics.
The young student believes her brother Martyn would have been thrilled with her results, too.
"He'd just be really proud," she said. "And he'd have been tweeting about it."