If her hocks are touching, she will probably always be built funky back there as she matures, and would not be a good choice for breeding or for any serious riding (in terms of athleticism or soundness). Some horses can be built fairly oddly in the hind end and be perfectly okay as light-duty "just for fun" rides, though. Others not so much. Depends partly on luck and largely on *exactly* how the horse is built and what the rest of her is like.
(edited to elaborate: if her hocks are touching but her hind cannons are parallel to each other when seen from behind and thus *they* touch, or virtually touch, all the way down to the fetlock, then that is not quite as bad IME as a horse with hocks touching but the cannons angled outwards so the fetlocks are a normal distance apart. The former is just a very very narrow, possibly significantly toed-out, horse; horses like that tend not to be super athletic and can have some soundness issues if asked to do serious hind end loading maneuvers such as collection, rollbacks, etc. But the latter, with the cannons forming sort of a triangle when seen from behind, is reeeaaaallly not good for strength or *soundness*, in my experience, and if it is more than just a slight thing, I would avoid buying a horse like that.)
If you are not looking for an athlete or broodmare, it couldn't hurt to at least get emailed some pics. I would not get too excited about the horse, though, as there are lots of free or cheap horses out there, and it costs as much (or more) to keep a horse with physical problems as it does to keep a strong sound one.
Good luck, have fun,
Pat