@Barbra Millicent No, not Hindi, just British English and Europe. Kelly Club was called Shelley Club, as seen on this UK computer game. This was in the early 2000s when Kelly was called Shelley, you weren't even alive
In the cartoon "Kelly's Dream Club" She had a friend named Chelsie, spelled differently from Chelsie. She is the redhead, and not related to Barbie.
There really wasn't a reason Kelly/Shelley became Chelsea, because she had never been called that before. My best theory is Chelsea is Kelly's middle name and for some reason she chose to go by that name.