Well, I've heard a method from another topic wherein the answer was the same as this one. "How to beat Charlotte". I had loads of problems with her myself, but this method made me own her ass to next Tuesday.
If you go down the destroyed stairs (that you may or may not have paid for to be fixed) you can find and catch Mienfoo and Bronzong with Heatproof Ability. You catch Mienfoo for Fake Out, although I think you need to have that move remembered, and you catch Bronzong to use the TM Trick Room on. That or two other Pokémon who can use these moves.
So what you do is: you Fake Out one of her Pokémon, I did it on Typhlosion, and hope that her Darmanitan kills the Mienfoo or that Bronzong survives. Afterwards you use Trick Room so that your slower Pokémon can hit first and then you kill the rest of her team with a Rhydon you can catch, or any other Pokémon that has damaging Rock/Ground attacks.