A fire element kamihime in a water team is particularly unfortunate because during the Water events, where you'll be running the hardest difficulty possible for essential drops, you'll be dealing with both debuff resistance AND elemental weakness on one of your characters. That's a nasty combo. A water element kamihime in a fire team wouldn't have this issue.
But Amaterasu does come with a 30% defense buff, so maybe that mitigates the problem a little? She'll still get hit hard.