Grass types are great options here, watch out for Ice Punch and Ice Beam though. I think you can get Tangrowth, Tsareena and Shiinotic at that point in the game, and all three of them are decent enough to use against Valarie.
Electric types might seem like an other good option, but the AI will switch to Lanturn with Volt Absorb or Seaking with Lightningrod when you use an Electric move. Electric types are still handy to use in this battle though; all of her Pokémon are weak to Electric besides Lanturn and Seaking.