Hear me out on this one before you get the pitchforks. There was once a girl that was liked and respected at her school, Ms. Regina George. Everyone knew her and wanted to be her friend. She even had a core group of friends that she was nice enough to drive around. They spent time together confiding all the things they would never have told to anyone else. Regina was so kind she even invited an odd new girl named Cady to the group. Cady was clueless about student life in a public school. Regina gave Cady friendship and in return, Cady sabotaged Regina's friendships and gas-lighted Regina into gaining so much weight she had to wear sweats.
Cady is the bad guy here let's be clear with that. Cady wanted to be popular like Regina but having no social standing of her own she took power by humiliation and constant undermining of Regina until it finally paid off in the form of stealing Regina's friends and claiming Regina's ex as her own in vomit. Cady's character didn't care about social justice for Janis and the ill-fated birthday snub. Cady just wanted to take Regina's top spot by attacking Regina in a non-confrontational, backhanded way. Cady wanted to be in the tacky Christmas performance because she wanted to be the girl that she saw being carried in gym class when she first met Regina. The problem Cady had to overcome was that she wasn't likable enough to be Regina and she knew it.
The true animosity for Regina that came from Cady started during the Halloween party that Cady embarrassed herself at. Cady went with a look that stood out immediately and badly. Realizing her error left her with a few choices; to go home altogether or change and go back, to tweak her look in the ladies' room there, or to continue with the look she already had on. Cady went with sticking it out as a ghoul, and she regretted it. Regina would have had the social graces to have never have made that mistake and Cady resented her for it. Aaron, unfortunately, was the person who symbolized to Cady if she was on the same social level as Regina. As likable as Aaron may have been, for Cady he was an ideal and not a person. The story left very little about the person that Aaron was explained. Aaron was polite to Cady and they shared a math class. Cady had no clue about this guy, for all she knew he could have had skid marks in his shorts and loved choke porn.
Popularity would never have lasted long for Cady. This is because Cady did not create popularity for herself, she created massive instability in order to be relevant. By taking the nuclear option she would have caused her own troubles. There are real-life history lessons that support my conclusion, look no further than Catherine of Aragon and Anne Boleyn. These women both had their fair share of problems before crossing paths. However, when Boleyn was able to manipulate her fantasy into reality. Yes, she had Catherine on the ropes but her own head was cut off once the dust settled after she became queen. Boleyn disrupted the whole kingdom to get her way, thinking that her tiny victories were just one good thing for her after another, when the truth was she was writing her own death warrant unknowingly. My point is that being a shady back-stabber might get you what you want, but it's not a true victory and it won't last. Cady would have had her own epic downfall in one way or another.