As far as I can tell it will be an alteration of Isabelle (in that spelling). "Belle" is "beautiful" in French, and "beau" is "handsome". Seems a little pointless to alter it though, but each to his/her own :)
We didnt personally alter it lol it is a variation that already exists :) Its no more pointless than AmiAimeeAmy Aymi or Macayla McKhaila Mickayla Michaela Mychaylah --------------then again you could be right :P