All dynamic cloth requires doing a little animation, even for stills. (The good side is you can pick which frame to use for your still, and thereby get the one which has the effect you want.)

I don't think it's the skirt that's the problem. There are lots of Poser long skirts. It seems harder to make loose and flowing tops than skirts. There are a few shirts with full sleeves, but they are often difficult to pose naturally. And the shirt itself is still close-fitting.

Image is Poserworld's nightgown for the PT Girl. It's the closest conforming nighty I've seen to Carib's.