Rihanna was created by a label. She was a girl who sang, but she wasn't an artist before being signed. The definition of manufacteured.
The same can definitely be said about Britney. She had a few years of a kinda-sorta creative freedom, but she was created by a label the same way as Rihanna.
People saying Gaga are silly. She was Gaga without a label, she started out with her own weird fashion and she was doing Pop on the LES before she was famous. She's self-created, really, and her label just gave her the opportunity to take it to the big time.