I'm going to offer a slightly different take on this subject, I've found in life that 20% of the people do 80% of the work. There's also an adage that applies here: "Grant me the strength to change the things that I can, and the grace to accept the things that I can't." I'm not saying that it is bad advice to confront her but I wouldn't be surprised if she never seems to fully pull her weight, even if she improves.
I would be very surprised if I learned that your leadership at school won't notice the issue when you're evaluated. Part of the point of group work is group dynamics, including group members that don't do their share.