Why does Rosalie want to be a human?

Answer 1

So she could have childeren, be able to do more, and move forward/grow old with Emmet, and have grand-childeren.

Answer 2

Rosalie from Twilight wants to be human because she longs to experience normal human activities like growing older, having children, and being able to eat and sleep. She sees being human as a way to regain a sense of humanity and connection to the human experience that she feels she's lost as a vampire.