Just go catch a Pikachu. Won't take 4 hours. A pickachu from viridian leveled against Mt Moon zubats for 10-30 minutes would wipe the floor with the whole gym.
That's not a bad plan, but it will require a new save. Once you enter Cerulean City, all the ways back to Viridian are blocked until after you beat Misty.
If you want to beat Misty without starting a new save, your best bet is probably to go north of Nugget Bridge and catch a Bellsprout. That should be about as effective as a Pikachu against Misty. If anything it might even be slightly better. Grass and Electric attacks are both 2x against Water types, but Water attacks are ½x against Grass types and 1x against Electric types.
I forgot Bellsprout had vine whip early and you couldn't go back. Oddish on red with absorb by comparison is a monumental pain in the ass. Absorb sucks. At least Pikachu is fast with thunderwave and can help you catch an Abra for your I win button.