Roxana, the weakest soldier in Persia’s elite army, is one mistake away from death. [At first, this line sounded fine. Having read your third paragraph though, would "is now only one mistake away from death" be more accurate? And the whole line might sound better something like this: "Roxana has long been looked down upon, as the weakest soldier in Persia's elite army. But now, she is only one mistake away from death."]
Cursed with the unique ability to transform emotions into weapons, Roxana can avoid bloodshed [should this be "can avoid her own blood being shed?] as long as she remains useful. Her only desires: to elude the general’s wrath and stay safe in Susa, [Isn't this just a single desire? To elude the general's wrath by staying safe in Susa?] the extravagant city of spices and gold.
When Roxana nearly kills the general’s son, she’s given one last mission to prove she’s worth more alive than dead. Roxana is assigned to guard Thessalus, the visiting Macedonian diplomat, who plans to secure peace in the form of a marriage alliance. Roxana must use her skills and cunning to unearth Thessalus’ true intentions. [Something's wrong with this whole paragraph. In the second sentence I'd say "She is assigned." In the third sentence, "But soon, through her skill and cunning, Roxana finds herself unearthing Thessalus's true intentions." She was never assigned to unearth his true intentions, was she? Only assigned to protect him, right?]
Nothing goes as planned, not even the course of her own heart. Thessalus and Roxana form an unbreakable bond as they dodge man-eating beetles and clairvoyant assassins. To Roxana’s surprise, she becomes more valuable to Thessalus than a mere human shield. [Here I'd say, "To Roxana's surprise, she sees she's valuable to Thessalus as more than a mere human shield."]
Then Roxana learns the truth: that Thessalus hides a secret that could turn the tide of war in Persia’s favor. If she betrays her own heart, she will become the savior of her country. Or she can choose to protect his secret and live with death on her hands. [I think I'd put this differently again. It feels disconnected from the previous paragraphs. Something like, "It is then, just when Roxana is feeling more useful and more hopeful about her prospects for the future than ever before, that she learns the truth: that Thessalus hides" etc.]
THE IMMORTAL GUARD, completed at 98,000 words is a YA historical fantasy and my debut novel. It is a reimagining of Roxana’s life, prior to becoming the wife to Alexander the Great. The events in this novel are loosely based on real incidents and people. My novel will appeal to fans of An Ember in the Ashes and A Wrath and the Dawn series.