I'm going to abandon my bullied friend
That's not very supportive of you to do, why would you abandon your friend?
Because she bullies someone I like at our school
You shouldn't be friends with a bully. They try to make life harder for other people.
I didn't think this through.
Even if your friend got bullied, it was not justified for her to bully other people, even if it is someone that you are not interested with. If you want to abandon her, it may not be the supportive thing to do, but it may be the healthier choice so that you don't get to end up being bullied by her in the end.