Am I a bad friend?

I have a friend group that consists of four people, including me. We are all good friends and go to the same school. One of the friends rarely comes to school, as she is often ill or has a migraine, fyi, she is at school about one day every two weeks. Once she is at school, she often just sits quietly and makes the atmosphere awkward and sad. When we have had plans to see each other, she often cancels at the last minute, which makes her a little bit unreliable. I have asked several times if she has any issues mentally but she just says that she is well. That fact that she cancels plans last minute, does not add anything to our conversations and rarely comes to school has led to the three of us in the rest of the group getting to know each other better and getting closer to each other and because she constantly says no to hanging out, we have stopped inviting her. Am I a bad friend?
Am I a bad friend?
Post Opinion