
In the first 2 episodes of s1, Rose is still figuring herself out and her outfits reflect that. In the words of Billie Piper herself, "the first time you see Rose she’s wearing these frumpy jeans and a baggy hoody top. It mirrors her life. She hasn’t decided who she is yet."
I think you can clearly see this in the end of world. The episode deals a lot with Rose not fitting in with the aliens and how unprepared she is to deal with adventures with the doctor yet.
Now, just for a comparison. Look at Rose's outfit next to the one Jabe is wearing. Jabe is much more confident and knows how to navigate this sort of places while Rose is clueless, and it shows.
Now, in The Unquiet Dead we can see a huge change in her costume. Yeah, it's a more historical one (not accurate but like are you really expecting accurate historical costumes from Doctor Who s1? I don't think they have a budget for that), she is wearing it because Rose is ++
making an effort to fit in. In the previous episode she was overwhelmed for most of it and didn't really try to get out of her comfort zone, but in this one she tries harder, and putting the effort of getting a more historical outfit shows that.
Now, let's jump to Dalek. In this episode Rose wears a white tank top. The more figure hugging silhouette shows how Rose is evolving and how she is getting more confident with herself, because of her time with the Doctor.
I think that making her wear white is an interesting choice here. She basically brings the Dalek back to life and shows mercy to it. As you can see, white is associated with innocence, purity and goodness, and I think her actions towards the Dalek highlight these traits in her.
Now one of Rose's most recognizable outfits: the one from The Long Game. So, as you can see in the second picture, Rose's outfit matches the scenario, my guess is that this was done purposefully because in the ep Rose was way more comfortable dealing with alien stuff.
Also, she was becoming more like the Doctor while she was trying to impress Adam, and there was an effort to make her look cooler and appear more natural in the scenario. As you can see, by this point the baggy clothes are gone and she adopts a more well fitted silhouette.
I dont have much to say about her costume in the empty child/the doctor dances in specific but this piece of dialogue is cool! It's basically an in-text confirmation of rose trying on new stuff and exploring more outfit options
The Boomtown one is very relevant in regards to her outfit to Mickey. Look at the outfit Mickey last saw Rose in and look at her in Boomtown. Rose changed a lot, and her costume shows that as well as her actions.
She knows who she is, what she wants and her life completely changed. Rose is confident enough to pull off a tighter clothes and a skirt, which is vastly different from her outfits before meeting the Doctor.
Her scarf is a bit similar to the one the 4 wore, but the colors fit more with Rose's color palette of mainly pinks, red, blues and purples, and it looks more affordable. In my opinion it's a reflection of how she is becoming more like the Doctor but she is still herself.
Now, to end series 1, her Bad Wolf costume. She has a similar silhouette to her The Long Game one, tight and red. She doesn't wear a red top because it looks good. She wears because after going through her character arc in s1, she is confident enough to do it.
Red represents passion, strength and defiance. She wears it on the peak of her power, as the Bad Wolf, when she challenged the Doctor and went back to save him, not only because she felt like it was the right thing to do, but because she loves him.
Forgot to add but Lucinda Wright was the costume designer for series 1! She did an amazing work, it's simply fantastic