The word <em>over </em>is used as an adverb in this sentence.
If the sentence said - There will be clouds over most of the country, then it would be a preposition.
Explanation:
One way to use slang and idioms in a story is to make characters feel more natural and funny. Unless a character is very formal, real people would not talk without slang or idioms.
Answer:
that she's done her research and dragons could possibly be real based on the evidence that she's gathered.
