Zalcano is an optional boss who isn’t required to be defeated for any quests or story missions. You could go through the entire game never fighting her if that is what you want, or you can fight her every day to try and get rare drops or sell the loot that she drops after she is slain. It’s really up to you about how you want to face this stone-coated demon. If you find her high-level drops interesting you can farm her, or you can simply forget she exists. No matter how you choose to play, do what makes you happiest.