It is ridiculous that they made such a huge issue about the bathroom break, provided there was no compromise in patient care.
As an OR nurse of 11 years who was trained by "battle axes", a word of advice.
I would not play the whole "the manager doesn't like me" card too openly in public. Unless the manager is universally despised, it will be spun in a manner that casts you in a somewhat unfavorable light.
Also, if your OR is like all the one's I have worked in, word got around the OR that the two newbies were having issues and couldn't hack the big case. Just understand the sword is double edged. While they may be talking about your manager, they are most likely also talking about you. If word got around that "her team" didn't know how to run the case, as part of the team, that reflects on you as well as the other team members and the manager. That is never a good thing to have going around about any team/room despite how it makes your manager look bad. OR nurses are notorious for baptisms by fire. If as a newbie you pass, you are golden. Perceived failure creates a whole different ball of wax.
Good luck in your endeavors. OR is a great specialty. The majority of OR nurses are tough nuts to crack but if you work them the right way, they are a wealth of knowledge.