I just beat Adrienne in one try with this Rainbow Field Team that I slowly built as the game progresses. Took me a while to come up with a finalized team but it might go through some more changes eventually.
"The Blooming Defense Core"
Meganium @ Light Clay
Ability: Leaf Guard
EVS: 252 HP, 252 SP.Def, 4 SP. Atk
Moves: Ancient Power, Giga Drain, Reflect, Light Screen
This girl is the core of my team being able to tank a Blizzard or Ice Beam from Aurorus without Screens Up. She really carried me