Is it okay to email a resignation letter for a nursing position?

Email is definitely acceptable, just be sure to include all necessary individuals in the email.

I always email my resignation letter and cc Human Resources so a copy is in my file. I think this has become a more acceptable practice and why kill a tree if you don't have too.

I would personally hand it in person. It's more professional and you know right then and there they're aware of your intentions. But if you are off the next day or few, email.