I didn't reply to that girl's text message twice. What happened?

There are several reasons. First, she really didn't see it. Your message may not have been sent to her mobile phone, or she doesn't have time to read short messages. Second, she doesn't like you, but she doesn't want to embarrass you and make you sad, so she ignores you. Third, she is testing you to see how much you like her and how you will chase her. Fourth, she is considering it. She may give you an answer after careful consideration.