Always found the idea of it being abuse when it comes to horses kind of strange!
If anything, especially when it comes to women with stallions? The women are the ones being abused!
And with men and mares? Well to put it bluntly I don't think there's a man out there who realistically compares to the size of dick mares are supposed to take! I think she'll be okay.
That and the fact if a horse doesn't like what you're doing you are gonna know about it... For about 2 seconds before you get bucked in the ribs and/or skull.