Your preceptor is supposed to check behind you in ALL of your tasks. It is just as much HER mistake as yours, and the fact that she wrote you up for it may just backfire on her. How are you supposed to know what course of action to take? That's why we put preceptors with new staff, for all that is good in the world!
I wouldn't sweat it too much. However, I can see how you will be more fearful of making a mistake, and less focused on what you are supposed to be learning as a result of this experience. If this is, in fact, a valid assumption on my part, it would be a good idea to nip this situation in the bud and talk to your NM face to face about what occurred. Own up to the mistake, but also express that you need clear cut expectations, and that you need your preceptor to provide you with that information. Had you known what steps to take to get the medication, this whole situation could have been avoided.
Just some advice: to start this process, email your NM and ask for a few minutes of his/her time to talk. When you are done with the discussion, email him/her with a 'follow up' email describing what you talked about. Give a short synopsis of what was discussed and end the email with "I want to ensure that I understand correctly your advice/direction/expectations. Is there anything else that you would like to add to what we discussed? Your goal is: 1. Clarification 2. Documentation of what was discussed. 3. Validation from your NM of the conversation, and since you ended the email with a question, a record of his/her reply will be in writing.
Documentation is your friend.
I would not broach the subject of getting a new preceptor. Let your NM make that call. Just present your side of the situation and let your NM decide what to do. Chances are the NM will either assign you another preceptor, or have a chat with your current preceptor. Do NOT own this, and don't think that you are 'ratting out' your preceptor. This is unusually harsh behavior, and it sounds like your preceptor needs a reality check. Don't get involved in that battle; it is the NM's responsibility to ensure that you have a complete and comprehensive orientation.
I am so sorry that you are experiencing this. It sucks. Hang in there, but be proactive. Keep us posted!
Hugs to you!