As a human she was being chased down by James like Bella but a vampire changed her before james could get to her and now she does not remember anything of her human life
When Alice was human..people were scared of her because she could see the future...so she was committed into an insane asylum...while she was there...James picked up on her scent..to him her scent was the same as Bellas' was to Edward...an older worker at the asylum (who was also a vampire) loved Alice and the only way to protect her from James was to turn her into a vampire too. She then escaped from the asylum and saw Japser and the Cullens in her future and set out on her way to find them... first Japser and then the Cullens.
