Ha. I see some Nala too. I'll try to take a higher road than I did with Nala.
I'm glad you quit that job, but it seems clear you have things to learn about part-time fast food/retail jobs while in school. Many of us have been in your shoes, so your situation is not unique. Most of those jobs suck, but can be a necessary evil if you're not 100% parentally funded.
some advice from both a parent and someone that was in your shoes.
1. Your school responsibilities come first, no question. This is something a student usually establishes during their interview. I'm guessing you didn't do that. Trying to get time off later without this set up in advance is a battle waiting to happen. You are 50% at fault if that's the case. She's a pizza store manager, she needs butts in place to operate that business. Of course she doesn't care. In the future, if you don't negotiate importance of school up front, and you end having another assignment due and they resist, you simply call in sick! Problem solved. If she fires you, so what? It's friggin' Pizza Hut, not a career job.
2. Yes, managers sometimes play favorites. They might be related somehow, could be the girl does everything she's asked to do without complaining, could be she's having sex with the gm, she could be racist; I don't know, I don't care, and it really doesn't matter. You're a part time employee. Just show up and do your dang job. If you hate it that much, you quit and find another job. But before accusing her of being a racist, remember she hired you and favoritism is not necessarily racist. And the fact you made her weight an issue, which is irrelevant, is childish. I'm sure you worked hard. But not every company operates perfectly in a perfect world. It's up to you to find a good fit, and not demand they change radically solely for your personal comfort, or give you constant praise/positive reinforcement for doing your job. There are no participation trophies at restaurant jobs. Again, if you hate it, you quit and move on.
3. As far as her not knowing the area? Also Irrelevant. In fact it's very common. She could've just moved into the area and had managed other Pizza Huts profitably. It just doesn't matter. fwiw my early post college managerial jobs required relocation. So why is that even a complaint?
4. Driving thru 3 school zones to get to work is pure whining, and has nothing to do with your employer. That's all on you. If you can't find a route around the schools during school hours, or won't leave a couple minutes earlier to compensate if there isn't, or are too stressed to drive thru school zones at all, then why on earth did you take that job in the first place? you knew the school zones were there. Sorry for being blunt.
5. I'd normally recommend manning up and quitting formally to her in person, instead of the unprofessional route of not showing up and sneaking away, as one should try to avoid burning bridges. It also gives you the chance to air your issues. But in this case, I think you probably spared yourself from being embarrassed by the GM by her citing the errors you made in an exit interview.
Listen, I'm not bashing you. You won't learn until you experience the many different kinds of life's curveballs. As a late teen, I hope you are starting to realize you do not yet have all the answers and begin accepting responsibility for your errors. And it seems clear you made some. I'm sure you'll eventually get there. But accepting you're not always right is a tough lesson especially for young males. You'll also eventually learn the only person that's right all the time will be your future wife.
Have you discussed this job stuff with your parents?? I suspect they probably had similar experiences when they were your age. I would think they are in a better position to help you navigate job related shark infested waters. Good luck.