Actually, no, I don’t think that seems excessive at all. I fall into the camp of if a person has owner and barn owner permission, signs waiver, etc., they should be able to ride the horse. However, in this case the second person didn’t have permission, hadn’t signed a waiver, etc. Just as some owners might get their hides a little chapped being told who can or can’t ride their horses, my hide would get REALLY chapped if some person that I never gave permission to came out to ride my horse. Actually, I’d be really annoyed with the person who had permission that they even thought that was acceptable and reconsider using her as a rider.
Does that seem excessive? Maybe. But I really am bugged when people think they can just do whatever they want. I mean that situation is way different than the situation described in the OP. (I’m sure some would beg to differ, but that’s how I see it anyway).