The same thing happened to me a few years back with my uncle and his girlfriend - his girlfriend was the one who knew what fluoxetine was.
It was a bit awkward to start with but later my uncle asked me a few questions and things got less uncomfortable when I explained a bit. He was worried to begin with but after talking a bit he went back to his joke-y self.
I think that it was more the unknowns that bothered him.

I don't think she will be focused on how she found out - seeming that worried about you, she will probably just want to be sure your ok. It will probably make your friendship stronger if anything
Good luck