Here's something that might help with expressions! It was my go-to for a long time. I think your problem right now is that you have a lot of the generi-expressions she talks about.
https://lackadaisy.foxprints.com/exhibit.php?exhibitid=333
As for the dialogue, I think it felt repetitive especially with the guard because he kept going "This vixen!" or "This bastard!" or whatever expletive. The more I think on it, I wonder if you're just including too much in dialogue? There's a lot of words that can be trimmed without losing what you're trying to convey.
Let's try this page:
I would rewrite it to be something like...
panel 1
Aku, thinking: ((What a handful...))
p2
Aku: Please allow me to apologize on her behalf!
Guard: Huh?! Why are you apologizing?
p3
Guard: You're not responsible for her actions!
p4
((remove the thought bubble from this panel))
Aku: No, but she's a friend and we're... working on it. (change expression to a nervous smile or something?)
Guard: Why even be friends with someone like that, though...
p5
Aku: ((Who knows. Maybe it's because when I first saw you...))
p6
Aku: ((You seemed so lonely.))
Aku: Shouldn't you return to your post?
Guard: Shoot, you're right!
Everything is shorter and you haven't lost anything! Plus, there's no need to explain how a character is feeling, just what they might say or think in that moment. Try saying the lines out loud when you write them and think to yourself, "Is that something I would say in conversation?"