Here are some options you could consider:
* Keeping it close to the original:
* Kelsey: This is the most straightforward option, as it's a common spelling variation of Kelsi.
* Finding a similar-sounding name:
* Céleste: This name means "heavenly" and has a similar sound to Kelsi.
* Kelsia: This is a variation that combines the sound of Kelsi with a common French ending.
Ultimately, the best way to choose a French name for Kelsi is to consider her personality, the meaning of the name, and what sounds best to you.