All interesting ideas here.
You can't magically convert a bunch of girls from loving what society tells them to do as young girls into liking science-engineering subjects. This takes numerous time and effort. As of where arduino stands in this battle, I wish I had an answer. What projects may interest young girls of that age?!
Very true.
female -> lillypad -> Leds on clothing
I personally think this is a poor idea that people seem to have. Maybe for a short time they might want clothing to light up but I think they'd be more interested on sewing material on to make the item of clothing look more like something made by gucci that something geeky that flashes.
Boys of a young(ish) age want to make things that move, blow things up, do things etc.
Girls of a young(ish) age (as said above) I can see being much more interested 'secret stuff', things that tell them something, hide something etc.
They are much harder to get interested in electronics, I do think that female presenters are a must - they really need someone of the same sex to get them properly interested and as a role model for them. As for specific projects, that's a hard one.
I started this:
http://collabedit.com/7cr9k
Feel free to change stuff around - lets see what people come up with. Stick your name in top right.
I'm a bit blank on ideas atm but I'll keep it open and try to add stuff when I think of it.
Ideally projects that use simple components and minimal coding but code could be mostly written beforehand and the students/children could have to modify pre-written code to do slightly different things or add to some pre-written code.