I find the reasoning behind this episode to be stupid. Just because they were bullied before doesn’t mean they should get off the hook, but this is still a kids show and there needs to be a happy ending. I did really like the song though.
Filthy Rich had always spent a lot of time around the Apples and tried to make Diamond socialize with Apple Bloom early on. However as Diamond Tiara showed more and more signs of developing into an lazy rich twit, her father wished she could be more like Apple Bloom. Thus, Diamond Tiara hates Apple Bloom for what she perceives as stealing her father’s love from her. This has made Tiara driven and competent (her ruthless management of the paper) but makes her more angry and hateful, the exact opposite if what her father wants.