How did Alice Cullen in twilight become a vampire?

Alice and her partner/friend (?), (who was an older vampire) were on the run from James. In order to save Alice, the older vampire changed her. In anger, James killed the older vampire. He left Alice alone, presumably because he couldn't fight a younger vampire. Alice can't remember because before the older vampire took she was in a mental asylum for her visions and surrounded by darkness, so the only past she would remember would be darkness. Also it has been a very long time.