To Cara, "Making an impression" meant dressing to impress. She couldn't get away with letting Rue wear those simple dresses that were in her closet. They might be suitable for a young dragon, but they weren't up to Cara's standards of flamboyance, and certainly not up to Rae's standards of quality.
The big sister would never forgive her if she found out that Cara had let an actual Princess wander around wearing clothes that she didn't make.
Rae had many Princess suitable dresses in her space, Cara was certain of it. The problem was that the spider was not here to tell her where anything was, and without her permission, Cara needed Karl to grab the stuff for her.
Dressing as a Princess wasn't something that Cara normally did, and she didn't have blanket permission to access the clothing, as Rae often saved pieces for specific people.
They did risk messing up that system when they grabbed stuff for Rue, but Rae should understand when they got back.
