I've heard about this theory, too. But I've always wondered, how Shin should turn to Zayin. As far as I know the two letters are not related or interchangeable in any way; at least not in Hebrew, I don't know about Phoenician. Or does the name Ishabel exist? All I can find in the bible is Eshba'al (1. Chr 8,33) and Ashbel (Gen 46,21), both masculine names.