My thoughts are in blue, words to delete are in red, suggested rephrasing is in orange.

Three years have passed since the Elvanian King and Queen were found dead in their bedchamber, slaughtered by the rebel group known as the Belladonnas. Nice, this is a good hook that has me interested and sets up the genre Two years since the newly crowned Child Queen invaded Marigold’s home of Muscain and turned the kingdom into a prison. Ten months since Marigold found her parents hanging at the gallows for treason. I don't dislike what you're doing here, style wise, but technically these aren't complete sentences. However, I don't think it's a big bump. I did have to untangle it a little on first read, but I think it works.

One week since her best friend Naomi went missing.

Having already lost everything else — her freedom, her home, her family — Marigold sets off to find Naomi. But her search hits an unexpected bump when a conversation in a tavern implicates her as the accomplice to the very criminal who assassinated the Elvanian Crown all those years ago. I don't know if three years could be described as "all those years ago." Suddenly, Marigold finds herself on the run from the Child Queen, tangled with a rag-tag group of fugitives led by a woman named Viana Nightshade.

Growing up, Marigold knew her as Red Hand — cold-blooded assassin and leader of the Belladonnas. But the more time she spends with Viana, the more she learns that fugitive isn’t all she seems. are you missing "the" before "fugitive?" The stories spun by the Child Queen hide the truth: Viana isn’t just a killer of Kings and Queens, but a daughter of them. A princess playing fugitive, caught on the precipice of a revolution she never meant to start.

A revolution that killed Marigold’s parents, and threatens to swallow Naomi whole.

BLOOD STAINED NIGHTSHADES is a 95,000 YA fantasy novel following five perspectives: the red-handed Princess, the soldier sent to hunt her down, the Prince who tried to save her, the Child Queen abandoned on a cruel throne, and the ordinary girl caught in their intricate web of Royal lies. It is the first in a series.

Hmmm.... so the query itself is great, but then I get to the last para and there are two POV's who aren't even mentioned in the query - the soldier and the Prince. If you're able to write the query without them mentioned, its possible you don't need their POV's in the book, either. I'd reconsider structuring this in a way that makes it possible for you to get all five named POV's mentioned. Also, are all of these POV's teenagers? If some are adults, I'd all this high fantasy, rather than YA.

And last note - YA fantasy is clogged right now, and pitching something as a first in a series is a tough sell as a debut. Consdier if you can structure the book as a standalone, with series potential.