She is saying that although she understands why you believe what you do, she doesn't agree with it. She sees it differently. She doesn't think you are lying or anything like that, she just has a different opinion about the situation. Your viewpoint, your mother's, and your T's are opinions, not facts. And so she can have a different opinion without "disbelieving" you. Your mother's opinion about you may be based on the wrong things. And your T's may be based on the right things. Your opinion is based on what you mother thought, so maybe yours is based on the wrong things, too.