Here are just some simple things to change
The part when the gaurds died was a little weird, I think you should have focused more on how 6 men had just died and hadn't jumped right into the self guilt. After something like that happens it usually takes a little bit for the person to experience much else but complete shock or anger depending who they are.
on the fouth page you say "Her sisters were gone" then a few sentences later you say "Two started pulling her away, down the corridor, away from the exit. Away from her sisters" How would she know if she was being pulled to or from her sisters if they aren't anywhere in sight. Like jjb said, the whole part with the separating needs a lot more work, for a few paragraphs I was wondering if she was under another flashback scene since everything drastically changed so quickly. Also why were they taking her to the courtyard?
They were there to take the castle. Jena had seen it almost two months ago, just like she had seen there would be no bloodshed
the bolded bit is a little hard to understand.
Her heart pounded in her chest, and she breathed in slowly a few times, trying to calm herself
That sentence felt a little like a list, maybe instead of saying how she breathed in slowly you can describe the breaths themself. for example - her breaths came in slowly, or something like that.
The outside force neared the courtyard, and leaned closer to the window, looking down over the area below
This sentence is pretty confusing, you mention the outside force which makes me think of the army but then you mention the window which snaps me back to the MC, I couldn't understand what you were talking about here.
And started pulling her back toward the courtyard.
this sentence was a little awkward in positioning.
She glanced out a window on the other side of the tower and noticed the lights on in the library
since its a castle and an army with swords is coming I'm assuming they don't have lightbulbs yet, so that means that the library was well lit at night with a lot of torches. It seems a little dangerous to have so mch fire with so much dry paper, you would think they closed the library at night or used single candle flames to light the way at night for midnight reading.
She flipped around, and saw five men run out of a passage into the courtyard.
the five men thing sort of threw me off, its like saying "He walked out into battle field to fight the approaching army of five thousand six hundred and two men." In a life and death situation, exact number counts seem akward. A simple 'few' or 'many' or 'half a dozen' usually works well (even though it specifies an exact number it still sounds nicer)
Overall it was pretty well written just that I need a little more from the characters and plot to make me more interested. Then there is the plot hole that kept on nagging me, if she thought it was all so dangerous and risky to stay in the castle then how come they didn't just leave the day before or something? Or at least send the women and children out just in case and the men could stay to defend.
It takes place in the same world? wasn't the other one like in present times?