Thanks everyone for the feedback. I've revised this with your comments in mind (for a third time). I think this is getting closer, but it's 264 words—perhaps a bit long?
Query revision 4:
When fourteen-year-old seamstress Jinxx Relinkerys deciphers a hidden note she finds in the castle, she possesses the evidence she needs to stop Lady Margaté plans to destroy Jinxx’s life. This feels a little too much like jumping in in the middle of things. My reaction isn't so much, "Oh, that's interesting," as, "Wait, who's Margaté and how and why does she want to destroy Jinxx's life?" However, a note isn’t strong enough proof to convict a noble. Fortunately, Jinxx is secretly studying magic. If she can learn how to use it in time, she might be able to save herself
Born with a deformity and dependent on crutches, Jinxx expected to be a seamstress until her math skills lead to an apprenticeship studying magic—something only few people know exists. Her life is like a dream This phrase just feels too blasé. Can you pick something a little stronger sounding? until Margaté, heiress to the local barony, struts into choir practice and starts to ruin Jinxx’s life. This is basically reiterating what you've already said in the hook. I realize that down below you start elaborating, but you need to get something going sooner, without repeating yourself. Actually, taking a step back and looking at things, just delete the first paragraph. That voids the repetition problem, and it deals with the issue I had with the hook before.
Margaté wants revenge for her father’s death and thinks Jinxx’s family is responsible. At first, Margaté restricts her bullying to choir practice, but it isn’t long before rumors begin to circulate that Jinxx’s close friendship with the local priest is inappropriate and scandalous.
Jinxx fears the rumors will reach her mentor Is the priest her mentor? Or is she close to the priest and learning magic from someone else? and end her apprenticeship. When Jinxx deciphers a note she finds in the castle, she’s certain it’s proof Margaté is spreading the rumors. However, accusing a noble requires much more than a note. Yeah, this only reinforces my thought that you should delete the first paragraph. This again is information you're presenting twice, and the query does just fine only learning it here. When a Jinxx finds a second coded note, she learns Margaté’s plans only start with rumors: violence is next.
Jinxx’s magic studies are all theory, not practice, but as a terrible sneak and even worse liar, she needs more than her sewing and math skills. To stop Margaté, Jinxx needs magic she can’t use.
Hmm. I think the big issue is that I'm not really feeling the stakes yet. I understand that Margaté is going to hurt Jinxx, but I don't feel the emotion behind it. Maybe it's that right now overall Margaté's threat feels very... petty, I guess. What is presented in the query is thus: Margaté is bullying Jinxx, and Jinxx might lose her apprenticeship because of it. And that's all unfortunate, but it doesn't come across as properly impactful. So two things that I think are worth playing up: the actual physical danger, and what Jinxx is getting out of her magic lessons. The magic's kind of a big deal, but honestly, for purposes of the query right now, it could be traded out for any hobby and nothing would really change. So can you give us a bit more on what the magic does and how Jinxx's life is changed by learning it? That will help make the reader care more that she might lose it.
Hope this helps. Good luck.