Definately all of the above, overall costs of a horse, feed, ect., but also learn about age. I have seen so many people these days going after the young horses, because of the idea that anything in its teens is too old to do anything, or because the idea of getting a young horse and working with it is cool, regardless of whether or not its a good fit. Some young horses can be very nice, and will be a good mount for someone that doesn't know much, but there are plenty who aren't, so don't let the number be the deciding factor. Also basic first aid, taking a temp, wrapping wounds, ect. And if and when she is actually ready to buy a horse, bring someone who KNOWS horses, and the horse world, to make sure that the eventual horse is a good fit, and that they aren't getting scammed because they are new to horses. I know that it saved my butt the first two horses I bought. I brought a friend who'd been doing horses for years when I was looking for my first horse, and there were several horses that she said don't even bother riding when we went to see them, because they were not what the ad said, or they had issues, ect., and again same thing when I looked for my second horse a few years later, I took my trainer, and ended up with an awesome horse that I may not have gotten if she hadn't been there.