I would have her checked out by a vet to make sure its rain rot. I mean rain rot is curable and I've known a couple people that thier horses had it. And one had to go ask the vet for a skin treatment , and the other it was very minor and had stuff to take care of it herself. If it is rain rot I wouldn't let it stop me from buying herr, if you liked everything else about her.
The only painful part of the disease for your horse is when you remove the scabs Depending how actually how bad it is.The actual infection itself doesn't cause your horse any pain or irritation -- not even any itchiness.
I found this transmitted info.
How is rain scald transmitted?
Rain scald, or rain rot, is transmitted a number of ways. It can be transmitted directly between horses, or it can be carried on items that are used on an infected horse then on another horse.
The most usual culprits for spreading rain scald (which is very contagious) are grooming tools. Prevention of this disease is just one reason its a good idea to have a set of grooming tools for each horse (besides, who doesn't need more grooming tools in lots of colors?!?).
Another common culprit is shared saddle blankets or pads. Or pretty much anything else that touches a horse's skin and is shared between horses.
It's important to keep in mind that horses can be carriers of this disease without showing symptoms...so a seemingly uninfected horse can still transmit it to another horse if he's simply carrying rain scald and not displaying symptoms.
Also important to note is that horses can re-infect themselves if the grooming tools and tack are not treated after every contact with the infected horse. Also treat any scratching areas such as trees or posts.
Best treated by first giving the horse a bath with soap to loosen and remove the scabs. Some people choose to use a medicated shampoo, while others simply use any regular shampoo.
Let the soap sit on the horse for a few minutes to loosen the scabs. After a bath, the area will need to be treated with something to get rid of the organism.
You can use a number of things, including antiseptic ointment or other remedies that are available at most feed and tack stores...many people recommend the Micro-Tek products.
Rain rot, rain scald, dew poisoning, or streptithricosis...whatever you want to call it, the disease is fairly easy to prevent, yet fairly common in the horse world.
It is actually the number one skin condition that affects horses!
Knowledge of what causes it, how to treat and prevent it, and underlying causes can help you more effectively battle this disease and prevent it in your horses.
Google it, articles, and stuff. It will tell you everything you need to know. :)
God created Quarter Horses, then he Painted the good ones! ;)