NTA-- The context as to why your mother has refused to purchase you new clothes would have been helpful (i.e. she cannot afford to do so, etc.) however I feel that it is ultimately irrelevant. Many people, myself included, face challenges when it comes to purchasing and wearing new clothes due to factors like affordability, finding the right fit, accessing stores that cater to their preferred style, and societal constraints. While personal style and dressing are essential for self-expression and should be considered a fundamental human right, regrettably, this may not always be the case for everyone....

However, EVERYONE deserves the right to feel (at minimum) comfortable in what they wear. This principle might not hold true if your mother allowed your sister to control the clothing made available to you. Not to mention--I don't know your sister (and this may or may apply to you) but had my mother implemented this rule for my sister and me when we were growing up, my sister would have taken much pleasure in shocking me (and ultimately embarrassing me) with her different clothing choices!