I would say if the 17 year old can purchase her own clothes with her own money she has earned, she should be allowed to do so. However, sometimes at 17 a girl does not know what is APPROPRIATE to wear to certain places, and her parents should guide her. My daughter is only ten and thought pajama pants and high heeled shoes were a good choice for grocery shopping. I guided her back to her room to change. Also, more seriously, sometimes teenage girls don't read the dress code for school or school events and every year there's a story about girls being sent home from prom for not meeting the dress code, so I think it's the parents job to help.