I am sorry to hear about this, but take it as a lesson learned. It is awful that your manager proceeded this way, doesn't sound very professional to have only one side of the story. If this buddy has quite a rep perhaps it was a way of making a sacraficial lamb for the other nurse, who wrote the letter. Trying to get at your buddy, but because you signed for doing flushes and feedings etc. she decided to be a jerk, maybe she was written up too who knows. In my opinion it was wrong for the nurse to even write the letter in the first place, she should have addressed this with you personally first. It is soo hard to be new and I know, I have not had the opportunity to stay in one place very long at all.
I am doing an ER orientation and although I love the ER, I find myself thinking, wow I want to run back to my old job because I fit in there. The nurses here are not as friendly, I see the codes come in and think I am never going to be able to function like the senior nurses do! IV starts and blood draws are new to me, and I have trouble getting blood. We were short last night I volunteered to go in thinking that I would be with my preceptor and I was on my own. I felt overwhelmed and scared. I am not going to give up just yet!! I hope that it will all click at some point, but the bottom line is that you should be treated fairly and talk to your supervisor, easier advice to give than to do I'll admit.
Try to hang in there a little longer but if you find this enviroment not conducive to you, then by all means find a new job there are many opportunities out there.
I wish you all the luck in the world, let us know how things progress, keep your chin up
Don't let one experience define the rest of your orientation!! Remember your co-workers were new once too!! They had to learn from experience as well!! Even if they forget that. These are the things that make us new nurses angry and frustrated.