I've noticed that we are slowly accepting things that we totally would NOT have accepted years ago. The gradual change from cute, classic children's clothing to the trampy "hip" clothes changes every year so slow that we don't even realize it! My issue is the Halloween costumes, since when does a 9-year old need to look like a slutty witch?
My stepdaughter wore what I secretly called a "slutty witch" costume that her mom bought her. It included fishnets, and she wore it with heeled black boots. The bodice was skin-tight and it had a short tutu skirt that showed her butt and it dipped low in the front and if she had breasts they would have showed. It was not my choice and not my child so I had to just go with it.
After Halloween my SD wanted to wear the fishnets with one of her regular skirts and I absolutely refused. I told her they were for Halloween only.
Once you okay something, it's forever okay. I think modesty should begin young so when they get older and they want to push the envelope you still have some room. If you okay everything when they are young, like fishnets, then what will she want to wear when she's older??
I hope your daughter does follow her dream of becoming a fashion designer. Perhaps her dream will lead her to create fun fashions for young people that are NOT revealing!