You ask:
"Wouldn't it have been better if after having gone to the meetings for a while and she had her consciousness raised and then took it upon herself to drop her himlines instead of someone dictating to her that she should drop them?"
The answer is no. It would have been better to have not gone to the kingdom hall in the first place. If anything, I would thank that elder for perminantly saving your daughter from the degredation of the Watchtower Bible and Tract Society. There is nothing wrong with medium to high hem lines and anyone who tells you otherwise has an agenda.