The Gym Leader is easy to beat. She mainly use's ghost type Pokemon. Ghost Pokemon are weak against Physic Pokemon. Trust me if i can beat her you can.
beat the gym leader
Pastoria city
Garitina appears after you beat the Elite Four. It will be under Hearthome city i believe.
you beat the gym leader
beat Fantina in the hearthome city gym
Beat Fantina in Hearthome City.
Go to hearthome city and beat the gym.
after you beat the 4 gym leader in hearthome city
go to hearthome city
After you get the HM and earn the Fantina in the Hearthome City Gym
just beat the fourth gym leader
You go to Hearthome city after you beat the league. Talk to Bebe and she will give you Eevee.