i've always heard the other characters talking about how she looks exactly like kitana, and i'm sittin here like wtf, no she doesn't (this is especially glaring in mileena's mk deception ending, when she apparently tricks all of kitana'a armies)
now she could legitimately be mistaken for kitana, excellent design choice
Very late to this party but now I'm here, I love the change personally
She is only half Tarkatan, so I guess it makes sense in ways for her mouth to be more human-looking. It also makes more sense with her being able to talk, since her having no lips in MK9 (in theory) should have really impeded her speech.
Slightly off topic but I also love what they did to her hair. It looks like an absolute ratbag, like a little girl who went crazy with a pair of scissors on her own hair, much to the horror of her parents... and it is SO Mileena it gives me life, I hope they continue with that theme in future designs.