So there are three ways of going about this:
First, as mentioned earlier is to have a Trick Room Team. You can use the Rock Types that you can get in the previous route after setting up Trick Room. Be careful, because Charlotte's Darmanitan has Superpower
Now the way that I defeated her was to set up Tailwind and Rain Dance. I believed I used Noivern in order to do this. Be careful, because Darmanitan has Rock Slide (you see the trend? It would be best to get rid of that Darmanitan ASAP) I used this in my 2nd playthrough in this game
The third way is using Pokemon that have Flash Fire (Arcanine). If you have X-Defense and X-SpDef use those. Be careful, because DARMANITAN. AGAIN. If I remember correctly, it also has Bulldoze...or Earthquake, so if you have an Air Balloon, that would be ideal. The Typhlosion shouldn't be an issue since it tends to spam Eruption.
You can also do a combination of some of these ideas. Hope this helps.