Should I be Getting Worried?

Leah was hoping to do some horseback riding tonight (it was postponed until tomorrow morning) but she has horses heavy on the brain right now. This afternoon on the way to Gramma's we passed a horse farm and she announced, "that's where I'll start work when I'm nine.") She has admitted that she'll probably be stuck with important but not so nice jobs like mucking stalls but she is pretty confident the owner will let her "just exercise" some horses some of the time. I guess there's a difference between expecting to be allowed to ride the horses and just exercising them.
In prepping for this experience she was told she needed to have a helmut in order to be allowed up on the horse. I told her a bike helmut would have to do and she was horrified, "can't you buy me a riding helmut?" She asked if she could wear her black pants (corduroy!), jacket and boots so she could be like a real horse rider. Yes, we were just visiting Spruce Meadows with their dress code :)

Tonight I was driving with just her and Sam and she informed him that Nana Lynn would probably allow her to ride all by herself. I reminded her she didn't know how to ride and so wouldn't be allowed but she insisted that she had ridden 4 times already and was sure she could do it by herself now. "Four times," I questioned? Yes, she had been led two times around the yard and once around the field when we lived by Gramma last year and she had been on a pony at the fair once too (she was still 3). Four times. And that experience was surely qualifying enough to make her a bona fide horse rider.
So, I decided a little scare tactic may be in order rather than arguing. "What if you want to stop," I asked, "how are you going to make the horse stop if you're by yourself?" She looked at me with the classic for-a-mom-you-sure-don't-know-much look. She crossed her arms, "I would say 'whoa'." "Well, what if the horse doesn't know about 'whoa'", I pushed. And then she rolled her eyes to the back of her head. "Of course he'd know 'whoa', that's horse language. All horses know that!"
I'm sorry, I couldn't help myself, I retorted with, "what if you accidently say 'trot'"?

It's for her own good, I'm sure she'll be safer if she has just a bit of fear!