Originally Posted by donatellodemerlieux
I don't even think I had turned all the way around before she released more than 1 bodily fluid.
This phrase mystifies me. Are you saying she urinated and defecated on herself out of fear?
As to the rest of your post, why wasn't she riding her own gelding? Couldn't she bring him?
It's not unusual for people who primarily ride only one horse to be nervous about riding an unfamiliar animal. They don't know the animal or its quirks, which can be extremely stressful.
If she wants to ride your mare again, I think you need to take it slow and let them become familiarized with each other. Have her do some ring work on the horse several rides before you go out into unfenced territory again. Being out in the open on a horse you don't normally ride can be very scary.