Ya know, just my take...

...but unless she has some riding skills and shows real horse savvy I wouldn't recommend a Shetland. They are super smart and can be little brats if the rider doesn't know what they are doing. Think of the issues that have been brought up here about horses testing their owners. That, in my experience, is a somewhat daily routine with shetlands. Now I'm not down on sheltlands, I had a lot of fun with several of them where I had my horse (well other than the aptly named "Bad Guy") but "not so high--not so far to fall" is not always the best adage! There are other ponies, slightly larger, that have more reliable temperments and your child will not outgrow them quickly either.

All the other advice given in other posts about chooseing an older horse for a young rider applies to ponies as well.