Tria is MUCH larger and heavier than Ms. Swimmer In addition, Tria has an inherent weapon (horns).
On the other side, Ms. Swimmer can probably evade easier and her tail can probably inflict serious injury. Not to mention, she can enter the water to evade Tria or use an improvised weapon like a large rock or a tree branch.
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I would say Ms. Swimmer even though it would be difficult. Yes, Tria can charge but that literally her only method of attack. Ms. Swimmer can tail whip, kick, throw objects or use a crude club. Not to mention she can probably evade better.
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Sue vs. LBT 1 Sharptooth