Because of the level cap, you cannot brute force her. You must use strategy:
If you find the game too easy or want an "Extreme" challenge, some players attempt a 75% Level Cap run, where you limit your team to three-quarters of the boss's level. AI responses may include mistakes. Learn more pokemon platinum nuzlocke level cap
If a Pokémon reaches or exceeds the cap before the battle, it is either boxed (benched) or not allowed to participate until the next badge increases the cap. Because of the level cap, you cannot brute force her