Being a new nurse is like being a small child learning to walk. Your preceptor can not always stop you from falling, but it is how you pick yourself up and learn from it that they are watching for. As a prector, I know my new nurses are going to get frustrated and that is ok, it's how they handle that frustration that I have to watch for because that helps me see how I can best help them through it.
In my unit, emergency psych, I also need to know that the new people have my back when I'm out there with a pt that could escalate to a violent situation. I have my newbies come out with me whenever I am dealing with these situations, so that they learn they need to be out there when things happen. Even if they just stand there as a physical presents, they need to be out there with me. The ones that run and hide in the bathroom when these things go down are ones that I know I can not trust to help me when I need it.
These new nurse that are scared out of their minds, and it happens from time to time, I kindly suggest that they might be happier on another unit. It is not safe for them or me. This is not bullying, this is for safety. If I have a pt attacking me, and they are nowhere to be found, well, I'm not going be really happy with them once all is said and done. I know this is for my unit and maybe your preceptor is seeing how you handle what is happening on your unit. She might be trying to make you better without you even realizing that's what she is doing.
Not all preceptors are great teachers, but you can learn from everyone, no matter if it is good, bad or ugly.
Best of luck as you move forward.