Let me start by first saying that any course of engineering is great for girls! I picked metallurgical engineering, because it was something I knew nothing about and I love learning. In fact there is still so much to learn about metallurgical engineering!!
In general, though, there are relatively fewer girls who study metallurgical engineering than other disciplines. When I was in college there were about 4 or 5 other girls studying metallurgical engineering that graduated with me, and about 20 boys. Although there is a lot of math, metallurgical engineering requires a good understanding of chemistry.
Most of the time, metallurgical engineers find jobs in maufacturing (steel mills or metals processing) or metallurgical labs (testing and forensics). I love working in a manufacturing setting, there is plenty of engineering and lots of interaction with the operators/workers. Not only does this allow me to exercise my engineering knowledge but it also allows me to develope my interpersonal skills and leadership techniques, both of which I think girls are inherently good at. Therefore, I think metallurgical engineering is a great choice for girls!