There's a lot to the story that I don't know about so I won't be making a judgment call. However, teenagers who've fallen into the rabbit hole of racism and bullying aren't easy to pull back. Whatever punishment you decide on, if it's as harsh as that, you need to be prepared for the possibility that it may completely alienate your kid for the rest of your life.
The point of punishing her shouldn't be for the sake of punishment, but rather to teach her how to become a better person. You can't teach her anything if she disappears from your life. I don't know you or her enough to know how she'll react.
Personally, I feel that cancelling prom wouldn't teach teenagers to stop bullying but it will teach them to hate their parents.
As for social media, instead of deleting the account and years of pictures, it would be better to deactivate the account in some way that doesn't entail permanent deletion, and give it back to her once she has learned her lesson.
I'm going to be blunt. The way you talk about punishment feels like an outlet for your anger. And you every right to be, given what she's done. But please remember that your daughter's behavior isn't set in stone. Take the steps that will actually rehabilitate her, not just punish her. Get her to write an apology letter, get her to post one last time on social media about what she did and issue an apology. Get her to offer an in person apology to the victim or parents (if that's what they want). Make her write an essay on the impact of bullying.
Whatever you decide to do, get her to stop the hate, not hate you for the rest of her life.