As a nurse, you are the advocate for your patient. You are also expected to follow MD orders, when those orders are not harmful to your patient. That's basic.
As an employee, you're expected to follow the protocols put in place by your employer, and submit to the authority listed as your supervisor, when doing so is not unethical, illegal, immoral, or harmful to yourself or your patients. Still pretty basic.
Where it gets complex is deciding exactly how much you hate power struggles, because by your own account, this isn't an isolated incident. Seems to me you've got three choices:
1. RUN. Find another job, because this lady *using term loosely* isn't going to change and one of these days, you're going to be screwed, and maybe sued, for ignoring MD orders in favor of policy or reprimanded, and maybe replaced, for ignoring policy in favor of MD orders. This is a no win situation and leaving may be the only way you don't come out on the losing end all the way around.
2. FIGHT. Document issues with your clinical coordinator, then file a complaint, working your way steadily to the top. Everybody but God's got a boss, or at least an agency providing oversight and accountability. This isn't a comfortable choice, but it may help patients and other staff. Plus, it's satisfying to see a bully get what they've got coming to them.
3. WAIT and SEE. How's that working so far? This is okay in the short term, and perhaps somebody else is already working on OPTION 2. Since you are the only nurse, I kinda doubt it.
Good luck to you!