This has been bugging me, but I remember reading this book about a boarding school where this girl suddenly gets a scholarship to. She turns up, and apparently she looks like this girl that disappeared/died recently. She eventually finds out that the board of directors and some of the students are sucking energy out of the students - her roommate is really tired all the time. I'm pretty sure it's a series.
This could be Secret Lives, first book of the Darke Academy series by Gabriella Poole.
The Darke Academy is a school like no other. An élite establishment that moves to an exotic new city every term, its students are impossibly beautiful, sophisticated and rich. And the more new scholarship girl Cassie Bell learns about the Academy, the more curious she becomes.
What sinister secrets are guarded by the Few — the select group of students who keep outsiders away? Who is the dark stranger prowling the corridors at night? And what really happened a year earlier, when the last scholarship girl died in mysterious circumstances?
One thing Cassie will discover is that a little knowledge may be a dangerous thing, but knowing too much can be deadly...
Never read myself, but the reviews mention a secret society of vampires removing life from the students, and it has the scholarship girl and mysterious death of a former student recently (apparently recounted in the opening chapter).