I'm planning on getting my four-and-a-half year old a pet . . . she's mature and good with animals. I have a 10 gallon tank and would rather not have to buy a new one. I'm leaning against a small animal like a mouse because I don't want it to get away and crawl under the couch while she's holding it. I'm leaning toward either a guinea pig or a bunny . . . any suggestions?