Marley, you are super into the slouchy look. And some (like Zap) are super into the sleek tight skinny look. Me, I put myself somewhere in between -- I can appreciate both looks, depending! I like to own some of each type. I do think some pants can be more or less successfully "sized up" in -- and others, mysteriously, cannot. It must depend to some extent on body type, fabrication, and the cut of the pants themselves. I have some that I have sized up in and love...and others that I tried to size up in, and they just looked dumb. Too loose overall...like I was wearing too big britches and no style or intentionality to it.
Now in this case I do think either size looks good on Sveta, but since they are supposed to be a skinny, I like the sleeker look of the smaller ones. But she does look goo either way! Lucky her.