You omitted the part in the diary entry about shooting up sheriff’s office

You're missing the part where it's a diary entry, so the actual content is irrelevant. Her only mistake was not realizing that her diary wasn't private.

Because it's not relevant. They're not charging her with conspiracy, which is what they would do if she'd actually done anything concrete towards making that happen. She didn't email it, or text it, or post it on Facebook or Twitter or Discord or a message board, which is what this law is clearly about.