Plagiarism itself is grossly unethical (very bad), but not a crime ... Violation of copyright is both criminal and civil offence but is usually treated as a civil matter.
Yes you can get arrested for plagiarism on anything.____The offence is not plagiarism but violation of copyright. In practice, this is usually treated as a civil matter.
Hmm... perhaps when you copy your own words and ideas from something that you own, so it looks like plagiarism but you actually have permission from yourself? :)
There's no way to answer this question - it all depends on the circumstances surrounding why you would be arrested AND why she would be there with you.