Nobody would voluntarily adopt stuttering. If you had speech therapy it's strange that your mother believes it's voluntary. At 24, although you're on the cusp of an independent life, it's still difficult for a mother to misunderstand your condition. My family was so embarrassed that I stuttered that they marginalized and psychologically abused me. Many times your parents can cause added issues. You’ll soon be on your own, and spend less time around her. I bet your fluency will improve.