Ultra Smart had those pijama/carpenter-like outfits, and i think some of the girls hiked one of the pants side up to their knee. not quite the same as short on one side/long on the other, but that's probably what you're thinking of Sohee.
during the one of HelloPro concerts (2012 winter, maybe?) with the outfits with lots of fringe/tassels, some girls had one side pants and one side shorts. they were all one color, but different girls wore a different color depending on their shuffle unit.. i think colors were: white, purple, pink, blue, red, yellow. i know Sayu wore red with a cowboy hat, Miya wore white and might have had the pant/short thing going on (which may also be what Sohee was thinking)?
edit: yep!
http://hossy0405.blog49.fc2.com/blog-entry-2077.htmledit2: going into detail isn't really relevant anymore, so just side-trivia at this point. Nakky and Chinami were the other girls who had one side shorts, the other side pants ->
http://pt9.blog134.fc2.com/blog-entry-1836.htmledit3: got one of the colors wrong. orange instead of yellow.