Well, I guess there are the girls who end up in the DA club, if it is shown any where near the level it is in the book, like Cho's friend who snitches, or Susan Bone's who asks about Harry's Patronos, although some have already been seen, I guess their parts might be expanded slightly.
Cho will be more prominent.
Luna of course (I don't see any way the director could cut her out - she is somewhat above being a minor character, who are easily cut, she has story elements, and plays a part in the character development of Neville and Harry, as well as being integral to the Quibbler/Harry interview development - although how will that work? The fall of Rita Skeeter was cut from The Goblet of Fire, as is her being an illegal animagus, and thus Hermione can't blackmail her into writing the article, can she?)
But yeah, the only new primary female student character I can think of is Luna (though Tonks will hopefully be about, even though she isn't really a student.)