By the way, her name is Fantina.
Considering the fact that she has Ghost-Type Pokemon, you can take a big risk and use a Ghost-Type Pokemon because like Dragon-Type, it is so powerful only it and another Type and beat it. Anyway, you can use a Pokemon like Drifloon or Murkrow/Misdreavis (Depending on game. Murkrow - Diamond. Misdreavis - Pearl), or use Psychic Pokemon such as Meditite or Chingling.
How to get:
Drifloon - Outside the Valley Windworks all day on a Friday.
Murkrow - Diamond/Misdreavis - Pearl- At night, inside and outside the Lost Tower(Below Solaceon Town)
Meditite - Outside Mt. Corronet, East of Enterna and many other places.
Chingling - Mt. Corronet (Between Enterna and Celestic town AND Cycle Road/Orebrough and Hearthome)
Ghost and dark type
the pokemon you could use to defeat her is electric types or rock and ice
with using a rock or ground type Pokemon, the best Pokemon you can use to defeat a electric type is rhyperior ok!?
teach a flying Pokemon defog and use it
You can use Pokemon like: Buizel, floatzel, gastrodon, and possibly finneon and lumineon
Ghost and dark type
pikachu,turtwig and aipom
There is are no certain Pokemon needed to defeat the elite four. Just use your strongest Pokemon.
The best way is to make sure you dont use any normal types moves, as they wont do a thing. Use a strong Pokemon for the lead, and have a well balanced team. Make sure you have plenty of potions with you. Just get rid of her Pokemon one by one, then for the last one give it all you have to defeat it.
Illuminati Gym. Use Your Micheal Jackson-Chu To Defeat Sir Barack Obama
answer is that you cant catch gallade in pearl only way is to get kirlia from platinum/emerald after you defeat champion and use dawn stone and it evolves into gallade.
the pokemon you could use to defeat her is electric types or rock and ice
Maylene (Veilstone City) uses Fighting-type pokemon. Use Flying or Psychic-type pokemon to defeat her. Wake (Pastoria City) uses Water-type pokemon. Use Grass or Electric-type pokemon to defeat him. I put Maylene and Wake on here cos you can battle both of them third.
You only get one from the leader of Team Galatic after you defeat him. (Unless you use cheats) Don't waste it on Palkia use it on Cressilia or Garintina.
you should use any high lvl ground or part ground Pokemon like golem or graveler and defeat all his Pokemon with ground moves because you wont get hurt unless he uses his normal types they only do little damage
with using a rock or ground type Pokemon, the best Pokemon you can use to defeat a electric type is rhyperior ok!?
If on Pokemon diamond or pearl you defeat wake the water type at pastoria city.Use grass type!If on platinum you defeat maylene the fight type at veilstone city!Use fly type!