I would definitely tie a red ribbon to her tail. And if someone is getting too close, it's YOUR job, again, to keep your herd safe, so tell that person to back off lol. Me, personally, I have no reservations about being "mean" to someone if they are getting too close and it could turn out to be a dangerous situation. It's not meant to be personal. Some people just don't have a lot of common sense when it comes to that kinda thing.
One thing you could try is everytime a horse comes up, reach down and rub and stroke her neck. I'm telling you, we use this on our horses if there is smack talk going on, and before you know it their ears perk up and their expression softens. It's like telling them that everything's okay. It's worked with our horses anyway.