What would be a good stage image for a woman with a green electric violin playing metal?

I would stay away from any cliche styles or fashions. As eclectic as a metal playing woman is, you should follow up with an eclectic fashion sense. Throw on what you like and what feels comfortable. If you notice, most musicians were what they like, not what they feel the crowd wants them to wear. Those who do aren't in it for the music, their in it for the popularity or fame.

Folk metal dress in my opinion.

http://www.tartareandesire.com/interviews/images/e...

Like the girl in that picture. That's the band ensiferum, by the way, if you don't know them. =)

Poison Ivy or Envee.