I've been thinking of the very same thing myself. There has to be a connection of some sort. I wonder how come Isabel became such a popular name from early on? People surely must've made the association to the wicked Jezebel. They say that Isabel comes from Italian and is a variant of Elisabeth (Elisabella -> Isabella). Then again, isn't the "bel" in Jezebel somehow related to the "bel" in Belzebub?