I think that if all preceptors put as much thought, effort and heart into teaching new grads as you have it would be a whole new world! She's very lucky to have you, no matter how things turn out, because you have her best interests at heart, not only as a future coworker, but as a person navigating a new and challenging career. It sounds like you are very consistent with positive and constructive feedback, and she's unlikely to be taken completely by surprise no matter how things turn out. Have you asked her how she feels that her orientation is going? Does she feel like she's where she should be, and what areas does she identify as weaknesses of hers?
As many other people have mentioned, sometimes things don't work out. It's not a judgment of a person, or their intelligence or capability as a whole, but not everyone is right for every work environment. Orientation is the time to figure out, for all parties involved, whether it's the right fit for all. No one really "fails" orientation, if it's just a matter of finding a better fit. I hope that the next few weeks feel productive for you, and for her, and you can all come to the best outcome.