Here is my second attempt at my query letter. I've changed the name from Spy Girl to Into the Shadows. Thanks for your help.
Sacha grew up on shooting ranges, Krav Maga crash mats, and the streets of foreign cities. Out of the blue, her father reveals the truth about her unusual upbringing: he is a spy. Now, he needs her to become one too. A rogue agent is on the verge of selling the identities of ten American NOCs—a list that includes her father’s name. But the traitor is in the wind and the only lead is her secret teenage son, Charlie. [Secret from whom? Everyone? I'd drop the word "secret," as he's obviously not secret to Sacha and her bosses.] [Consider starting a new paragraph with the next sentence.] Despite feeling betrayed by her father’s lies, Sacha chooses to leave the security of her normal life [Her normal life hanging out with her buds on shooting ranges, Krav Maga crash mats, and the streets of foreign cities.] and step into the world of espionage. If she can keep her cool long enough to [and] keep her cover, she [just] might just be able to complete [accomplish] her mission: to spy on [monitor] Charlie’s actions and communications and follow the intel to the rogue agent.
To succeed, Sacha needs to infiltrate Kingston Preparatory Boarding School in Paris, home of the next generation of European diplomats and politicians. But Sacha wears Chucks not Chanel, and she’s better at fighting than fitting in. Add to that a politically-driven school principal and her target’s [Charlie's] snarky French girlfriend getting in the way of [hampering] her mission, and Sacha begins to think her handler might be right – she should stick to school and leave spying to the adults. But time is running out, and Sacha is the only option left.
Into the Shadows is a 55,000-word, stand-alone YA novel with the potential to grow into a series. I have worked for the past eight years as a writer and editor of children’s books, with more than 30 books published by Pub #1 and Pub #2. This is my first YA novel. A few other agents are also considering this submission. [No need to say this if you're referring to just the query letter.] Thank you for your time.
This sounds pretty good to me.
Is NOC a common-enough acronym that the literary agent will be familiar with it? If not you could go with "agents" (in which case you might change "rogue agent" to "traitor).
While "more than 30 books published" is impressive, it almost feels like an exaggeration. The reader may wonder why someone with 30 books published doesn't already have an agent. If that number includes both edited and written works, I'd reduce to the number of which you are the author.