Isabel (and all it's variants) is actually Jezebel (איזבל -- ’Ízebel), which is Phœnician; it might mean "Where Is The Prince (Lofty One, that is to say)". I am not persuaded that it is derived from the Castilian Spanish form of Elizabeth as BehindTheName.com suggests; in Ladíno, the Castilian dialect of Səfā́rodim Jews, it is rendered Ýsabel.
It certainly does not mean 'dung', technically speaking. Considering nevertheless the possible meaning "Where Is The Prince?", which is to assert "There Is No Prince" (as another website defines this name as denoting), it makes sense that BehindTheName.com renders Jezebel as meaning "Not Exalted": given that in ancient ages sons were valued more than daughters, as male heirs were the ones to carry on a family's line, if a man (or family) had a daughter but no son this manfamily was consequently viewed as having nothing (that is, mere waste) to their lineage. I speculate that perchance this was the case with King EthBä'äl of Tsídón (or Sīdon) [note that reference here is drawn from God's Word the Bible (or haTanakh) @ 1Kings 16:29-33, the first recorded usage of the name Isabel], that is to say he had a princess yet no prince: 'where is the prince', thus? 'there is no prince', his royal line is 'not exalted'. His daughter would amount to mere waste in connection with imperial legacy. Princess JezebelIsabel may have been designated her name on this account. In EthBä'äl’s giving of the princess as wife to unruly King Äħā́v, the nation of Tsídón came into profound paganish-political partnership with holy Yisraël; perhaps in this way Isabel was of royal function to her father.
The last three Latin letters (or two in the Hebrew) of IsabelJezebel can possibly be a reference to the demon-deity BélBä'äl (AkkadianSəmitic for master, lord, owner), though I'm not assured of just how possible it is that the name in its entirety means Daughter of BélBä'äl as suggested by this website. One would think, if that were the case, that the name would sound something like 'Batbel' (Master’s Daughter).