plagiarism is often very hard to prove if you've just used other people's ideas or the odd phrase. However, copying and pasting whole paragraphs is definitely plagiarism. As hc4361 says, it's the intellectual property of the original writer (or anyone he or she may have assigned it to).
If anyone finds out, Margaret could be sued or banned from the fair. Always credit the original source - or even better, study it so you understand it fully and then express it in your own words.