I can't really say this to her; it would be infantile. I need to be very grown-up when I confront her. So I shall rant here. Feel free to ignore a very angry post.
"X - what right did you think you had to walk into my horse's box and cut, yes CUT, his mane? You don't work at the yard; nobody asked you to do this. But you took it upon your interfering self to mutilate MY horse. The mane looks TERRIBLE. It looks as though a child has been at it with a pair of blunt scissors. You know full well that a mane should never, ever, be cut. It should be pulled*. You have always considered yourself to be something of an expert, so you should know this. Blue has (had) a lovely mane. It didn't need anything done to it. I am furious (I rarely get very angry, but this time I am).
"I didn't know what to do with all this anger, so I'm spilling it out onto my blog, which I'm quite sure you've never even heard of, never mind read. When I see you, I shall try very hard to be civilised, but you will sulk, which is what you always do if anyone annoys you. But I don't do the sulking thing because it's childish. I shall be the bigger person (I actually am the bigger person, being several inches taller than you). I shall try to control myself as best I can. And hope very much that you can find some explanation for your extraordinary behaviour. (What I would really like to do is go into your horse's box and cut his mane OFF. But I shan't. Sadly.)"
I shall probably see X tomorrow. I'll let you know how adult/ sensible I manage to be....
*Anyone in the know will know that a horse's mane is never cut; the hair is pulled out in such a way as to leave a natural looking line. This does not hurt the horse!