This is highly questionable. It is not at all clear that you are supposed to do something your parent wants when it does not directly affect the parent.
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To Popa et al who disagree with me (which is fine with me, btw), Who are we to judge what “directly affects the parent?” Many parents are EXTREMELY affected directly when they are frum already, and their kids go even more right-wing (even if it is only in such an area of dress codes).
When their frum daughter suddenly feels that two-four inches or more below the knee, are not tzniusdig, it may cause concern to that parent that the child is becoming a “fanatic,” (though I personally believe four inches longer than knee length is reasonable, and I like it even longer, aesthetically). I use that expression, because it is the one that an acquaintance of mine said to me when describing her daughter upon her return from Seminary. The family has nothing of which to be ashamed in their religious hashkafa, but all of a sudden it is not “good enough” for the daughter. And that IS hurtful to a frum parent, whether or not you might agree.
Rashi specified in his explanation on the phrase of “Ish emo v’aviv tira-u” being followed by “V’es Shabsosai tishmoru,” that a person must always show respect and awe for his parents with ONE main exception, and that is if the parent asks him to do something contrary to the Torah, such as Chillul Shabbos. It does not say anything about listening to the parent, unless the inyan does not really directly affect the parent. In any case, we are not talking about Chillul Shabbos, but about a girl who wants to wear clothing much longer than usual, which is apparently embarrassing to the mom who also dresses b’tznius (unless she does not, in which case that is a different story and all bets are off).
A mamin, I have a reply to your comments, but I have decided that in the interest of not making it appear that I have something against people who want to grow religiously, that I will wisely refrain. Not everything people choose to do makes them, as you said, “more than” their parents. But they think it does, and therein lies the rub. In any case, I think children of frum parents have a Torah obligation to listen to them, if there is no religious contra-indication to doing so.