What should I do about my autistic friend?

Even if she did commit suicide, it wouldn't be your fault, becuase she chose to carryout that decision. Even her saying such negative things like that would automatically push me away and motivate me to stay away. I would tell her guardian about these worries before I go though becuase autism can be really tough to live with. If she just doesn't get it (since you've already tried to explain to her) the only thing you can do is just ignore her. don't answer her text. Try not to bump into her where she'll know you'll be. Take other routes around school. if she's coming, act like you have a phone call.