[hisnameispip]

I have some experience with gerbils, and in my opinion they do marvelously in glass aquariums. They really don't need a ton of space, but too little space is bad as well. A good rule of thumb for the minimum is 10 gallons per pair of gerbils, but I keep my two boys in a 20 gal. Gerbils are very high energy and jumpy, and honestly could be too much for a young girl. My 6 yr old brother gets overwhelmed by my gerbils quite often. Also, they are a bit difficult to tame. I'm going to echo what Serendipity said- a Syrian hamster would be a lovely option. They do sleep more, but are very easy to tame, don't move too quickly, and kids love them. I had one when I was a little girl and I have one now. I think that she would be old enough to understand the concept of a pet and to be able to hold a hamster in her hands, or pet it from your hands, once it was tamed of course. The decision is yours, but that is my recommendation.