A Siren with only Water Attacks and no creatures maybe.
Plants are generally Hydro Immune, so most Water attacks (except Acid Ball) are useless. Also, Water Elemental is useless.
Plants don't Bleed, so that nerfs the Deptonnes and Undead Pirates. Ditto for Coral Reef wall.
Plants can't be moved, so Merrens aren't any good. Ditto for Bed of Urchins. Similarly, most of Grapple is irrelevant (aside from the attack dice modifier). And the most popular songs don't do much because Plants can't move, and Uproot isn't mandatory.
So... with rare exception, Sirens have few tricks available vs Druid.
Of course, a Siren can play out-of-school attacks, but you're already suggesting Fire spells are no good vs Plants, so I don't know what you have in mind. As far as I can tell, you're just trolling at this point.