What I would do with her, is re-teach her (or just teach her) to stop based off of your seat.
When you are asking your horse to stop, there should be a progression of your aides. It's not exactly fair to ask your horse to go from run to stop with no warning. So for instance if I am cantering along and I want to stop first what I will do is sit deep in my saddle letting my weight fall down through my legs so I feel heavy in the saddle. My position stays the same, but I am letting my weight sit more so the horse learns that means I want him to slow.
If he ignores that, I may add a "whoa". If he ignores that, I will do a few half halts on the rein, and then pick up being a little more 'loud' with my aides.
This isn't something you should just start from a canter. If you teach this at a walk, it will be much easier to translate to the canter.
If you feel your horse isn't stopping, I don't recommend running him into a wall or fence. I've seen quite a few injuries happen that way. Instead if you can, I like to put them on a circle and spiral down ward. Pick up on your inside rein and push his hip to the outside of the circle.
At a walk or a trot, you can try a one rein stop, but I really don't like them for anything faster because I feel like you can off balance the horse too easily.