I like a university teacher. Recently, she was ill. I asked her about her illness on qq and said I was worried about her. She didn't reply to me when she saw it, and then I sent it again.

Teachers must understand your short-term meaning and that you are "interested" in her. However, she may feel inappropriate or at the wrong time, and will reply to your message selectively. If you really like her, try to see the effect for a while and give the teacher a time to think or feel.