If Joyce and Natalie are best friends Joyce might standup for the bully this is because friends love, care, respect and stand in for each other. If she is her best friend, she will try to defend her friend and stop the bully because she love and care for her friend. Good friends don't like seeing each other in pains and they tend to protect each other. Because Joyce value their friendship she will try to protect her friend and standup to the bully so that her friend will not be attack or oppress again.
