That info definitely influence's my answer.
For riding with a 7 year old in the park i can't imagine the need for more than 3 gears. If you've got it to spend, go for it. But.... a good LBS will let her take it for a test ride, definitely do that. Ride with her if you can and make sure she uses the way she would have on your trail. If she likes it, wrap it up.
Be like "The Beaner", do whatever it takes to get her riding.