Derived from the Old Norse word kildr, meaning "a spring [of water]," Kelda is a name that sounds like you've probably heard it somewhere before - but haven't. Pronounced KEL-duh, like Zelda with a K. However, it is not a name regularly used in any Nordic countries. There is a chance that any usage of the name is more closely tied to -lda ending names in general, like the trend of -n or -ella ending names today (Braeden, Lexibella, etc), which would mean someone took a name like Kelsey and combined it with the ending of names like Zelda. It is more likely it comes from the Northern English word keld, also meaning "a spring," which would explain where and how often it has been used. Upon first glance it also seems like a Germanic name, along the lines of Hilda, and the Norse kildr is cognate with German quell of the same meaning. However, its usage could have started from a surname referencing where that person was from, just like Winston or Colton. This would also make sense if it came from the English keld. That doesn't mean it isn't usable - many names originated as place names or surnames and are popular given names today. Kelsey and Chelsea are two examples. I can't speculate any further than this, but Kelda does seem easily accessible in multiple languages.
Kelda Roys is an American politician, and there is a Kelda in the Thor comic series (pictured above).