^ I believe having just one actress for Selene is the way to go. When she over exerts her powers and ages they can use computers to make the actress age, and then go back to being young when she absorbs someone's life force.
Bellucci is gorgeous, but Selene needs to be a younger actress. Michela Quattrociocche could be good. Sasha Grey? Isn't she a pron star? Um... no, that won't work...
For some reason I could see Michele Rodriguez in this role:
Here is a scary one... could Angelena Jolie pull it off?