She was scared - it's likely we don't yet know what all her dad did to her...
pretty sure its more about he wanted to do,but didn't get the chance to due to her power.
as for why Marina didn't help Cat,it might be because if she did the principal would likely also detain her/send her to the farm.
where her parents could find her,although i'm not if sure her father is looking for her as proactively as her mother.
people get way more selfish and stupid in such a situation,especially if it would require self sacrifice when there is a easy route out.
good thing it was just a "could've been scenario" if it wasn't for the MC,so no need to really deep dive into it.