If you are just looking after her until she is sold, why not just lunge her?
You have no stake in this horse, you were not asked to train her, just exersize her, right? Then why risk injury to yourself or the horse?
That's true, you do need to get back on no matter what. .
Errrr no you don't need to get on no matter what, you don't HAVE to ride and for sure you don't HAVE to ride a horse that isn't yours and that scares you that much.
I see it from a different view, first of all you were scared and you got an and rode her anyway, so that is a victory in my book, I say congratulations for getting on her not once but twice.
I truly think we need to remember that riding should be fun, there are a lot of us that ride even though we are scared, but there is a huge difference between being nervous scared, as I am most of the time, and being flat out crying and shaking scared. You can work yourself through the jitters, through nerves, through a lot of things, but true terror, then not so easy.
You don't get on with every person that you meet, you aren't going to get on with every horse that you interact with, I've ridden horses that I didn't like, I've ridden horses who I didn't click with, I often ride though I'm scared, BUT I WILL NEVER ride a horse that makes me terrified.