Props to you for getting out of there, some times it is best to move onto greener pastures. I don't think there is anything wrong with giving your horse a pat if done right. I go out with my horses and just chill with them, I know their personalities and they know me. One of my mares is this big, husky thing, (okay, ALL of my mares are big, husky things, but one in particular,) and she is actually fairly 'sensitive'. She doesn't need hard cues and corrections, but she does need to be told when she is doing a good job. If I praise her, she'll lick her lips and sigh a few seconds after. I was riding her the other day and I gave her some good pats on the shoulder and butt and she knew it was praise. Other people will go up to my horses and smack them hard, and they don't enjoy it near as much. I guess it is about the nature of the pat, and how much you coddle them. And I guess what knowledge you were brought up with.
While I'm not a devout Parelli follower, my trainer was and she was a good horsewoman, teacher, and not condescending in the least. A lot of people dislike Parelli, but honestly it sounds like you were dealing with a self-righteous cowgirl who over stepped her bounds. The worst part is, she might of actually believed being an annoyance was going to change anyone.