You know the stereotypical scenario of the husband comes home, finds out his wife hasn't cooked him dinner, so he loses it and screams at her? He screams at her because in his mind he worked all day, he's tired, and the fact that his wife didn't cook him dinner means in his head that she doesn't love him, so he lashes out. She knows he's explosive and what his expectations are, so she should know better than to fail him. It doesn't matter if the wife has been slaving away every day at her own full time job, managing the household, bathing the kids and giving her husband nightly back-rubs. Tonight there's no dinner and that shakes the husband's vision of the ideal - how the world is supposed to be if his wife truly loved him. If his wife truly loved him, she would have found time to make dinner no matter what. She failed, so she deserves what she gets.
If you really loved your girlfriend, you'd be texting her back whenever she texts you; you wouldn't 'forget' about her, even if something important came up. That'd be like abandonment. You wouldn't be coming back from bars at 4 AM. You'd say "Screw my grades and classes, I'm coming to see you this weekend even if all we do is sleep." You'd pay her attention and make her feel special instead of grieving for your dad. At least that's what your girlfriend's vision of the ideal is. Like the husband above, it's delusional.
You are a normal person with a normal idea of what reality is - Reality A. This is where most of us are. Your girlfriend has a different idea of reality, one where you must jump through hoops to show her you love her, or pay the consequences - Reality B.
Because your girlfriend's idea of how things should be is not normal, you will always be at risk of inadvertently setting her off. And when she gets upset, no amount of reasoning, defending or pleading is going to work, because she's in illogical Reality B where the rules are different and you just messed up.
The only way you should respond to someone being illogical is a "Knock it off!" or "Stop!" or "I'm NOT putting up with this" and a timeout. Anything else, and you are going to get sucked into their nonsense. The responses you give her in the context of Reality A she will twist into something different in her Reality B and you will have to keep fighting. YOU know the reactions your girlfriend is having is illogical, Reality B-type nonsense, so 1) Know it's nothing you're doing wrong, and 2) don't put up with it. Tell her to stop, take a break, dump her, whatever you need to do.
You don't say how much you love your GF. I think if your GF ever wanted to change, she could, but getting her to see she needs to change may be a different story. You're both pretty young, there is no reason you should sign up for a lifetime of this. She may change, she may not, but you are going through a tough time with your loss and then school, so you certainly don't need this kind of negativity in your life. If anything, dumping your GF would do her a favor - she'd learn men won't put up with her nonsense.