She grunted in pain but refused to let go of the creature. "Die!" She bit it harder.

The creature tries to escape, but you but through its natural armor and killed it. Zach steps back, hands to his head.
"I'm sorry!" He yelps. " I don't know what's gotten into me. "

(I'm picturing Selene right now as like a dog or cat that killed something and brought it to you and is so proud of themselves.)
She spit it out and shapeshifted back. "It's not your fault, Zach." She tried to calm him down and held her side. "I'm fine, I swear."

"No you're not fine! You holding your side is a sign that you aren't fine!" Zach says, gesturing to everything yet nothing at once as he freaks out. "I am the worst friend ever!"

She put one finger onto his lips. "Shut up. I'm fine. Let's continue on." She grimaced before trying to drag Zach along with her.

Zach follows you, silent for once.
There were no signs of any more monsters yet. The first monster had resulted in the first death and injury. Who knew what the second would bring? Zach was wishing at the moment that he could turn back time or heal or being people from the dead.

When she let go of Zach she put her hand on her side. I'll have such a bruise tomorrow. If I'm not lucky, I'll have internal bleeding. "Zach, you need to stop beating yourself up because of Charlotte's death. You were being controlled. It's not like you could've done anything in that moment."

"I could have! I could have stopped being mind controlled! I'm sorry I hurt you." Zach says mournfully.

Selene turned around and hugged him. "You need to stop blaming yourself, okay?"

"I have stopped blaming myself." Zach objects, hugging you back gently.