Used Trek 820 Mountain Bike
It is a Trek 820 - new they are about $525.
This is a small 16" bike. Probably 5' and up. Very low standover, so may fit a smaller young teen-ish person. It is a WSD - women's specific design - which means wider saddle and narrower bar which I believe would be welcome for anyone this size, riding this kind of bike.
This bicycle has been refurbished to the Blue Tag standard which includes a 30 day warranty. For more on Coco's color coded refurb standards, click.Coco's is a local bike shop, primarily selling local bikes. Dis-assembly, packing and shipping adds a hefty $150.