She was infested with internal / external parasites and covered in rain rot. (tulsapetsmagazine.com)
Cases of rain rot can heal on their own, but it is recommended that you treat them to keep it from worsening and to prevent further damage to the skin and coat (absorbine.com)
The horse suffered from lice, a prolapsed penis from frostbite, and a bacterial skin infection known as rain rot. (abajournal.com)