Hell hath no fury like a woman scorned. Oh, how true this is. When Sam cheated on and left Leah, a woman was left in the dust along with the remnants of what was once a hopeful future. It wasn't Leah. It was Faith Uley. Sam's mother.
Leah Clearwater and Rosalie Hale are NOT friends. They simply tolerate each other. However, they both have people they don't like but can't complain about to anyone else.