Emma Jacks, aka EJ12, is an agent with SHINE.
That, both she and we are told by "an old-ish lady with long white hair whipped up into a slightly messy bun with a few pencils sticking out of it", is an underground agency, to which Jacks points out was sort of obvious since they had just taken an elevator 20 floors beneath the city surface.
The first part of SHINE that Jacks is shown is a large room full of women at computers or talking on headsets, all "solving problems and stopping evil plans" which is what SHINE does and why it needs someone like jacks even though Jacks is just 10 years old!
"'We need clever thinkers, especially people who love maths, and it doesn't matter how old they are. We need agents to help us crack enemy codes and thwart the evil missions of the SHADOW agency. We defeat SHADOW,' A1 explained, 'by intercepting their secret messages, getting to their locations before their own agents and foiling their dastardly plans.'" A1, obviously, was the old-ish lady.
Jacks was being introduced to the organization because her school had been one of many participants in a country-wide primary school maths competition and she had entered and won! Jacks was excited just to take part because "she loved maths and loved solving problems" and actually winning and getting a trip with her mom to the big city was so cool!
And from that moment on, she would no longer be just an "average ten-year-old girl" but also "EJ12 - a field agent and ace code-cracker in the under-twelve division of SHINE... And while Emma Jacks often found it hard to deal with mean girls, irritating brothers and other everyday problems, EJ12 was unbeatable. Compared to dealing with mean girls at school, saving the world was easy!"
"Since that day, EJ12 - or just EJ, as she was called when she was on duty - had foiled evil plans all over the world. She had jumped out of planes, dived into oceans and climbed mountains. She had cracked some of the trickiest codes around and beaten SHADOW time after time. In fact, EJ12 had quickly become one of SHINE' s Shining Stars, a leader in the agency's Spy of the Year competition."