I still haven't spent much time playing with every girl.
The only female character I've training with and playing as is Sindel and I can say she's a very hard choice to pick for n00bs when it comes to combos. You can projectile a lot yes, but combo-wise, she's not easy at all, even now I'm still having trouble with her.
Kitana I found the easiest, very MK2 to me. Sonya is not that hard, but a bit more complicated than Kitana. Mileena surprisingly, I haven't her hard at all, right there with Kitana and Sonya.
The easiest: Kitana, Sonya, Mileena.
The hardest: Sheeva, Jade, Sindel.