Meaning: A young female child came across or discovered a small, round piece of metal used as money in a lower position than a piece of furniture for sitting on.
Choice of Words: The word "girl" refers to a young female child. "Found" means to come across or discover something that was lost or hidden. "Coin" refers to a small, round piece of metal used as money. "Under" means in a lower position than something else. "Couch" is a piece of furniture for sitting on.