I think you should let your friend know how much it’s bothering you, that it’s affecting your studies and sleep. I think once she sees that you’re struggling with the situation, she’ll she that your comment wasn’t genuine and was intended as a joke. I think you should apologies again and stress that it wasn’t meant to be serious or hurtful and that you’re sorry you hurt her. But in the future, refrain from making similar jokes as it obviously doesn’t sit well with her.