Both origins are correct. "
Isabel" is a Latin form of
Elizabeth, and can be found in various forms in languages such as Spanish, Italian, French, and Catalan. However, it also exists in a form completely unrelated to
Elizabeth (
Elisheva in Hebrew), as a dialectal variant of
Jezebel. Just claim the first origin, and not the second one, if you want to use
Isabel.
The Wikipedia pages for both
Isabel and
Jezebel explain this.
Hope that helped!