My sister is very introverted and thinks she is too ignorant. I really don't know what to do.

This is not a question of introversion or not. We introverts don't carry this pot.

Your sister's behavior is actually a matter of quality and morality. I think it is probably the lack of family education and the lack of attention on campus.

You can start with her recent study and life, and then go deeper step by step, such as her views and attitudes towards her family, get to know her better and slowly set out the topic.