The 15-year-old Appaloosa Arab cross had lived in the paddock for about a year and had never been hurt before.
The incident had been "horrible'' but she did not believe someone had planned to harm the animal.
"It is a worst nightmare. But I don't think it was set out to be malicious - it was just somebody who didn't think about it.''
While she could only speculate, she believed someone, likely to be a child, had been visiting the horse for some time.
A wooden mounting block had been moved to different spots in the paddock.
"They obviously care about horses to begin with, because that is why they enjoy being with them. Which leads me to the fact they didn't mean for it to happen.''
Swelling and cuts would heal, but Ms Sygrove was concerned about emotional trauma.
"She is a very friendly horse but psychologically, or emotionally, we don't know what is going to happen. I haven't put a rope near her yet.''
The police had been contacted.
"I just hope those involved realise this is not how you treat horses,'' she said.