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.
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There are many times in a human’s life that they're given warnings that signal their soul is in a vulnerable state. It’s at these times that a battle is raging on between two forces that are invisible to the human eye. When the guardian angels Should this be possessive? side wins, you hear stories of humans escaping death. When Cendall’s side wins, there is no story to tell. Some call them the angels of death. She prefers reaper, but if you want to be technical you can throw the word grim in front of her name. Humans view them as the evil, but there are two sides to every story. This is well written and interesting, but you're not actually talking about your book here, you're simply saying that Cendall is a reaper. It can be established much more succinctly. I like your first line about instinct kicking for humans - maybe consider remodeling this to be your hook and melding it with what you have in the first para.
Cendall thought her biggest challenge was being the only female to ever finish training, and earn the title of grim reaper. See, we're in the last para of your query here, and just now learning what your book is about. Establish that Cendall is the "bad" side, then move on with your plot sooner. Though nothing could have prepared her for the unique challenge of collecting Lacie’s soul. Her soul is protected by multiple guardians, wanted by demons, and she can do the impossible: see Cendall. This is a very convoluted sentence. Tease out the details that you're trying to cram in here and give them more of the space that you used up above establishing Cendall's identity. It's a soul that screams, "extremely experienced reaper needed", but Cendall refuses to ask for help, afraid it would make her look unfit for the job. This ends up being the first mistake in a long list of reaper rules broken. That leaves Cendall blackmailed into working with her natural born enemy, to protect a soul that she’ll eventually need to check off her list. Interesting - I really like the idea that the reaper ends up protecting the target and it's not a romance angle. But I've lost your plot entirely here in the last para - how does she end up blackmailed? Why is she protecting Lacie and how does she actually feel about it? Are they friends? Or is she just protecting her because of the blackmail?
DEATH HAS A DAUGHTER is young adult paranormal novel complete at 61,000 words. Thank you for your time and consideration.
I think you have an interesting twist on the guardian angel story given that it's about friendship and not romance. As I said before though, you need to give more space to explaining your plot and less about establishing Cendall's identity. There's enough angel literature out there that your reader will know what a reaper is without you having to explain it so much, which will free up space for the necessary plot explanations.