Wow ! I hope this lady is not raising children in this manner ! I think we have to establish boundaries for our horses and act like an alpha mare or "Mommy" mare would. By this I mean the owner not only needs to separate and warn others of her horses' inclination to bite, but also needs to smack her with a crop in the chest or neck as the mare is lunging or showing any aggression. By allowing the mare to do this, in my opinion, she is "training " her that is is acceptable. I hope your friend is okay, I had a stallion latch onto my leg while riding with a friend side By side years ago. I kept a good 6 feet of distance, and was riding a quiet gelding, but he waited for an opportunity and grabbed my quad muscle. The bruising lasted for months, but luckily it was mostly sore on top, so I could still ride. Also- I think this rider with the mare could be blackballed from rides for allowing the horse to do this. Happy Trails ! - Heidi Helly