A good place to start on the machine side would be Apple's refurbished store. All these machines come with the same warranty as a new machine, and can be extended to 3 years with AppleCare. They are "used" but reconditioned by Apple to ensure no issues exist.

http://www.apple.com/shop/browse/home/specialdeals is the refurb/clearance part of the store. Inventory changes often, and for her use, a MacBook Air 13 inch would likely be ideal.