Since she is a single-target attacker, Capy will only target the nearest Cat unit, but Capy does insane damage to the Cat that she attacks. She has huge DPS and 15% chance for a Critical Hit, so there is no way to tank her attacks without your tankers going down in seconds. She also has 335 range, so meatshielding and using ranged attackers is the way to fight her.
Chew well and go to a hot spring until you can
Soaking. Movement speed is faster than it looks
It's slow. Occasional crit shoots.
She is very easy to stall with meatshields, as she is a single-target attacker. However, if she is supported by bosses like Teacher Bun Bun, the latter can wipe out all the shields for Capy, allowing her to hit stronger cat units (notably in Oil Platform and Morning Rush Hour).
There is no difference between EraserCatvariants and other 75¢ meatshields getting one-shotted, so bringing 75¢ meatshields is recommended over the former. Kyubey Cat is also useful against Capy due to their 40% chance to survive a lethal strike.
Strong Up combos on Crazed Fish and Island Cat work greatly against a single Capy, and fantastically against multiple, if meatshielded properly.