I have a mother who married into an entire community of home schoolers like you describe. I am familiar with the life long Biblical perception that it's not OK to draw attention through dress IN GENERAL as well as not dressing provocatively in a sexual way. The girls in the family all dress sort of like quakers, though some of them do actually wear jeans. We also live in an area with lots of Amish who have the same beliefs, so I understand. I get it. I feel weird going to visit my mom sometimes in -as my mom now calls them-"modern clothes" and make up.
This is particularly strange to me, since I am 40, and she married into this family 15 years ago, therefore I wasn't raised that way. Suddenly, in my 20's she started commenting on my "lipstick". WHAT??!! Or saying I shouldn't wear "such tight pants" EWWW, WHAT??! Normal fitted jeans??! I was raised riding horses in jeans!!! Seemed like a pervy observation to start with, but she takes it a bit overboard compared to the rest of the family. I was shocked after having a mom who bought Avon and got her hair done her whole life, to see her with gray hair down to her waist braided into a bun looking 30 years older than all the other grandparents her age, but hey, her choice. But would she REALLY be a wayward hussy if she kept herself up a bit more in accordance with 2011? I'm not asking her to wear bikinis and stripper heels, but surely some make up wouldn't hurt...But then I realized, I was being just as judgmental as her, so I don't say anything, and I take the comments she gives and let them roll off my back.
ANYWAY! When I was a teen, it was the 80's, and my peers didn't dress in a slutty manner with micro mini's as a staple like now, but we did dress pretty weird. I had a passion for weird fashion and became a fashion designer and moved to New York and worked in the garment industry for 15 years. It was hard work, and I didn't appreciate the implication from my mom's new side of the family that because I was a fashion designer for a living who liked clothes, that I was also and immoral, deceived, superficial person of non substance, trying to draw attention to myself for the sake of evil. It's just a bit much. Some of the most wonderful selfless people I know dress well and make themselves look good. The two qualities are not mutually exclusive.
For your daughter, it is very impressive that she goes against the norm by dressing differently than her peers when most kids just want to fit in. Even though I dressed very strangely, a lot of my friends did, so it wasn't so "brave". I can see where this would worry you that she is focusing too much on her exterior, but I would not worry about that unless she starts to lack morals or lags in other parts of her life. If she is still a wonderful person, then it would be you focusing too much on the exterior. As far as your spiritual beliefs on the matter, I think you should keep it at skimpy or provocative clothes. There really is no harm in just dressing formally. She will find her own way, she's only 14. Thank goodness she's not going around town in her pajama bottoms like the kids do today.....(woops, now who's the judgy grannie? :)
Don't stifle her in the clothing department if she is flourishing. That will drive a wedge into your relationship with her. Do your best to love her style and even help her dress up. It's not a fight worth fighting. She won't be a better person for dressing more plainly. It truly is what's on the inside that counts.