Meet my Hatchet of Death (or, some other colorful description RC Lewis and I come up with at any given moment). This is how I edit myself, it is how I edit others. If you think you want to play with me and my hatchet, shoot us an email.
We all know the first line of a query is your "hook." I call the last line the "sinker." You want it to punch them in the face, in a nice, friendly kind of way that makes them unable to forget you after having read the 300 other queries in their inbox.
If you're looking for query advice, but are slightly intimidated by my claws, blade, or just my rolling googly-eyes, check out the query critique boards over at AgentQueryConnect. This is where I got my start, with advice from people smarter than me. Don't be afraid to ask for help with the most critical first step of your writing journey - the query. My comments appear in green.
When Amanda Bennett took a job at the cult rehabilitation camp that had helped her deprogram, she didn't expect to get caught up in a whirlwind of events designed to bring about the end of the world. Oh cool. You've definitely got my attention with the concept, but I do think that the opening sentence itself is a bit longish. That could be personal opinion though. Boyfriend, best friend, and trusted director; someone has nefarious intentions and it's up to her to find out who. I think you need to use "or" instead of "and" in the previous sentence, unless the b/f, best friend, and director are all the same person.
DIAMOND DUST is a 50,000 young adult novella definitely don't call it a novella. It can be a novel with that word count and there's no traditional market for novellas with a paranormal twist. It follows the story of Amanda Bennett you don't need to use her full name twice, a young woman working at the cult deprogramming center Camp Invicta. Previously a member of the local Janus cult “New Beginnings,” Amanda's journal entries show first hand knowledge when it comes to what these kids have experienced. Amanda is reassigned and no longer working beside her best friend, Marie Davenport. Again you don't need to use proper names in a query except for your MC. It's her best friend, that's all we need to know. It's all good because that means she can spend time with her resident crush, Assistant Director David Lennon same thing here. It becomes evident that Camp Invicta isn't what it appears to be. Several campers have gone missing after graduation, including Amanda's friend Annissa. Pieces fall into place that make Amanda afraid that someone is attempting to sacrifice these kids to raise The Keres, ancient Greek vulture women. Someone close to her has been lying the entire time. Someone she cares about will die.
I'm a 27 year old military spouse and stay at home mom to two rambunctious boys. A book lover my entire life, writing has always been something important to me. This is my first full length story. I wouldn't worry about including a bio if I were you. If your bio isn't relevant to the novel content and you don't have previous publishing experience I would skip it.
You have a really interesting concept here that sounds pretty original. There's nothing specifically wrong with the query, but I would consider restructuring. A lot of the material in your body paragraph is reiterating what you used in your hook, but in more detail. Also, it's not clear how raising the Keres could bring about the end of the world, which is a big part of your hook. Also you mention your MC's reassignment, but it's not clear what she was doing first, what she's been reassigned to, or what that move has to do with the plot. You've got a good body to work with, just do some restructuring and you can have a strong query.