Wear whatever you are comfortable in. If you're comfortable with what you're wearing, you'll have confidence during the interview.
Just use some common sense. If you're dressed up as if you're going for a night out in the city, it's going to leave people with the impression that you're a party girl and they won't take you as seriously. You'd better have an amazing application.
Likewise, if you're dressed so conservatively that you're uncomfortable, or it stifles your outgoing personality, you'll blend in too much and hurt your chances. The interview process allows us to look for people who we can work with for 5 years and people who will represent our organization to patients in a positive manner.
Remember, even the male applicants are choosing their ties carefully and ironing their clothes the night before too...