St. Jude...the patron saint of LOST CAUSES is my go-to saint! Not that raising little girls is a lost cause...but sometimes it FEELS that way!!
My step daughter just turned 9 in April...where once she would wear whatever I put out and submit to having her done however I wanted to do it...she's gone and gotten OPINIONS.
This is not good for my controlling nature!
But this is what I resigned myself to...
As long as Sally is following the house rules (being kind, respectful, responsible and using your manners) then I won't fuss too much about how she chooses to do her hair. Sometimes I don't give her a choice...but usually I don't bother with her hair as long as it's brushed. (which is being responsible for herself!) I don't even mention her hair and how it would look cuter THIS way but FINE if she wants it to just be boring...which a lot of people do thinking they are backing off but really are just adding to the power struggle!
When Sally realized that I wasn't going to say a word about her hair AT ALL as long as she brushed it, she started ASKING me to do things with her hair. Once they realize you are not going to enter into a power struggle with them, they don't feel the need to RESIST so hard. Those power struggles are hard to avoid and they are usually the heart of the issue. They want control of things and rebelling makes them feel like their voice is being heard. It's sad when they are no longer little girls. *sigh*
If your DD is fussing and pouting b/c you are doing her sisters hair, I would remind her that she made it quite clear that she wanted you to keep your hands out of her hair and if you are going to respect her wishes on that end, she needs to be respectful on hers and nix the pouting! If she wants something done with her hair, all she needs to do is ask! That puts her in the position of taking responsibility for her choice and makes it clear that you will not be entering into a power struggle with her. That should put an end to it...if it doesn't, then you start talking about consequences for disrespectful behavior. (that's the sequence in our house anyway!)
Same with clothes...I have final veto power, but usually I let Sally pick out her clothing...unless we are at Disney...or going somewhere fancy.

I'd ask your DD if she wants some customs...High School Musical, Hannah Montana...those are my step daughters favorites at the moment...if she says no, which she may out of reflex, then I'd just say okay and totally drop it. She'll most likely stew on it for a bit...and maybe surprise you when she comes back and asks for something.
I do behavioral stuff for a living...so sorry if this was long and rambling.
Seriously...St. Jude...he's a good one!!!