Correct. This is retcon. In BG2, she uses vampirism to escape her shortened lifespan after having her elven heritage magical stripped from her as punishment in assisting Irenicus drain the Tree of Life.
While we're on the topic, I was never entirely sure what
exactly that "elven heritage" was supposed to be in its totality, though. Was it just their long life span (basically a delayed death sentence) or their... emotions or what else? Irenicus wants the Bhaalspawn's divine essence to "restore" himself before he goes play lumberjack again, but obviously he was still quite powerful to begin with.
When talking to Ellesime, he says he was "stripped of everything that was elven", but it would be helpful if we knew just what that "elven" means. You know, other than "longsword fodder."