Once you fixed the Power Plant, go to the end of Route 25. Talk to Misty and she'll return to the gym. Then you can beat her. (She uses water Pokemon so I suggest you use grass or electric Pokemon.)
at the end of the cerulean cape (route 25)
Misty is located around Bill's House at the Cerulean Cape, but you won't find her until you finish solving the problem at the Power Plant.
You best the rest of the Kanto Gym Leaders. Since they are challenged in no particular order, Misty may be your Seventh challenge. If this is so, then you go to Cinnibar Island, where you find Blue (Gary Oak's game counterpart). He is the Viridian Gym Leader, and you take your 8th gym challenge. If Misty isn't your 7th challenge, then you beat the other gym leaders before you can challenge Blue.
beat the 8th gym
you need to beat jasmine in olivine city
After you defeat Misty, You can go catch suicune by Bill`s house.
You can go and challenge other Gym Leaders in the Kanto region, such as Brock.
you go to the power plant talk to everybody there go to mistys gym after that and there will be a man in black there beat him in a battle and then go to the side of house there you will see misty.
After you beat all of the kanto gyms, go to cerulean city and go to where you saw misty with her "date". Suicune will be waiting there.
During your first battle against Misty in PokÃ©mon SoulSilver, you can use Electric attacs against all of her PokÃ©mon except for Quagsire. You need to use a Grass attack or a Flying-type attack against Quagsire.
misty will be a gym leader in HeartGold and SoulSilver
Misty is at the Cerulean Cape. It's close to Cerulean City.
Misty has a 49 Golduck 49 Quasire 52 lapras and 54 starmie
you need to get the kanto power plant and talk to the manager then you go to misty's gym and find a team rocket grunt you follow him and beat him then you find the machine part and return it to the power plant then go to bill's house then go up the hill next to it then you see misty
you go on the route right of fuchia city on the side closest to the sea, restore power to the power plant, and beat misty and he should appear
She's at the end of route 25