I'm impressed that she came to visit him for so many years. I think the others are right that she's moved on emotionally and is satisfied that her horse has found a good home.
I bought my first horse just a few months ago. It was a bit of a strange situation in that the horse had an owner for ~4 years who was forced to sell him back to the breeder due to financial problems. The breeder put me in touch with the former owner, who clearly had a very strong bond with him. I did offer that should could come and visit him, and I genuinely mean it, but I'm more than 3 hours from her, so I don't know if she ever will.