he's not trying to be mean, he's just scared. things are going to be weird until he can solve the problem. try to be nice to her.
Your sister needs help from a therapist. Encourage her to go to a school councilor to explore her options. That's the problem you need to deal with first and foremost. You can live without TV.
Usually, they are available, and if not, any teacher can also help. Also know that in many communities there are public centers that offer free mental health care and therapy. How old is your sister?