If she is turned out where there are bushes with thorns, it could also be a thorn. I live in TX now and have some mesquite trees in my pasture and my solid paint filly had a thorn in something that looked like that. (I found out when just running it over with water, and some linement didn't bring it down. poked around and squeezed, the end came out barely, and after some rather uncomfortable squishing for the horse, i was able to grab it and pull it out. It disappeared a couple days later with me washing out the small wound for a couple days and meds.