If you don't reply to her text messages, you just don't care about her in her eyes.

SMS is a tool for two people to communicate. If she sends you a message, she still wants it back. If you don't feel the need to reply, you will ignore her feelings. She may think that you don't care about her because she is waiting for you to reply to her message. So after receiving the information, even one or two meaningless replies may be a comfort to her!