I make this assessment completely unbaised. I have never seen any of her films, and though she looks the part, I can't say I approve. Most of the actors cast either have little prior to Twilight, or a lot of minor roles. And that makes the overall feel that much better, it's easier to imagine the actors as the characters, without straying back to "Well... this is different than when they were in such-and-such movie".
Too many of the teen crowd would remember her as Gabriella, and those that haven't read the books might be caught off guard at how Leah's attitude differs.
Stick with the down low crowd, casting directors, it work in your favor.
No offense Vanessa Hudgens.