Clutterfunky

Haha! good luck with the Magcargo if you do, it easily gets two-shot , that's why I said it was a last resort. If you're willing to take the chance like I did, Flare Blitz will one-shot that Alolan Sandslash as well as almost take out the Ninetales. I don't remember exactly what I did, but my winning run went something like 
Donphan -> Earthquake (which will knock out both of the pokemon, since Sturdy prevents the Glaceon from KOing it but Earthquake alone won't KO the Glaceon, the shattering glass does; as well as the Donphan

Rapidash -> Flare Blitz, one hit KO (I don't remember the pokemon, just that it one shot it)

Rapidash -> Flare Blitz, one hit KO on the Alolan Sandslash

Rapidash -> Flare Blitz, takes Ninetales down to red but KOs the Rapidash

Talonflame -> Flame Charge, KOs the Alolan Ninetales

and I don't remember much from there, I think I used my Talonflame until it got knocked out and then used Arcanine to finish off the fifth pokemon, used Flare Blitz again because the Arcanine was going to get knocked out so I may as well use everything, then finished it off with Lava Pume from Magcargo.

So like, mostly spamming Flare Blitz to win because who needs strategy lmao

Also why did you take a Drapion into that fight, isn't it weak to her Pokemon

Ah, good ol' fire spam...there's a reason Charlotte's known as the hardest boss in the game. TBQH I didn't think Dash had the stats to really do well here, but I guess flare blitz really helps there, and TBH I tend to underestimate it since it's available from the aqua gang quest so early on.

I barely even thought about fire types, since I was transitioning between Camerupt (slow, ice-neutral) and Volcarona (mystery egg, evolves at level 59 lmao) at the time. I was just so dead-set on the mirror shot plan that I didn't see other options....which happens more than I'd like. Fun fact, you used to be able to get Magnemite before Shade; Magneton's great SpAtk+STAB Mirror Shot made a joke out of her whole gym.

I actually did end up breaking the field (with Flygon) for Bennet, who managed to be a pain regardless. My sort of slow, auto-damage-heavy bulky offense style does NOT deal well with 5 setup sweepers hahaha. Even with 4x effective Power Gem, Ampharos just got worn down by repeated signal beams.