From the experts:
Carleigh, a fancier way of spelling Carly, reflects the trend toward trying to make an ordinary name more special by fiddling with the spelling. Yes, Leigh is a feminine way to spell Lee, so Carleigh is theoretically an acceptable way to spell Carly, but it doesn't really work that way. People will wonder: is it Car-lay? Car-lee-uh? And your child will forever have to spell her name. Stick with Carly....or better, Carla or Carlin, or better yet, Charlotte or Caroline.