The reason why their relationship is less than perfect is an extremely confusing set of things. Like there is a nickname Carter uses that I made no mention of because it would just invite more questions. Like the closest I can give to it is that he's not quite used to actually trusting people, and is not used to having a sister in the first place.
But also... what is he supposed to do in this situation character-wise? Like... here's the scene, with him running away removed:
She finds a woman who is covered in spiders and on the floor with a broken leg.
"Turn back. You shouldn't be here."
—
Penny gasped and backed away.
Carter walks towards this woman.
—
"She'll ruin you... she'll ruin us all."
Carter is trying to rearrange her leg into shape
—
A bone snaps out and it's an insect.
—
She collapses and becomes a mass of spiders.
Penny falls over and backs away.
Carter is trying desperately to keep her form together.
—
She grabs him and pulls him away, while he tries to get her off of him.
Carter: What are you doing? get off me!
Penny: She's already gone!
—
He shoved her away and _____
What would you fill that blank space with? What would make more sense for this character to do story wise? (Both characters are 12 years old to be clear, since you asked, and also there is a swarm of insects crawling right towards him to eat his skin)