When it comes to rivalries, I’ve always preferred the ones that can be characterized by one character smiling and one frowning. When both smile, it suggests something of a friendly rivalry, like one based around a game or sport. When both frown, it suggests more of a hostile rivalry, one fueled by an undying, mutual hatred of one another. When you get one of each, it suggests a rivalry that’s completely infested with conflict and that the two of them are so wholly incompatible with one another that they can’t even agree on how they feel about each other.
 
And yes, these therapy sessions were Twilight Sparkle’s idea.