Your team has one simple problem:
Damage ~
It looks like you should change a lot of pokemon to make a more decent team,
First of all Pyumukku is an okay defensive pokemon, but his potential is very limited,if you can stall your opponents it is somehow viable but against Charlotte it is lacking what you expect from a water type pokemon,It can't hit back at all,very risky against Charlotte,
You crucially need a stronger water pokemon to beat her,(yes rain dance and stall is a good strategy but nothing you have can make a dent on her team),like Milotic,Blastoise,Vaporeon
You have to hit a little harder to bring her down,
Golem has no reliable recovery options that's why he is not good enough to be a wall,also his low special defense is a deadweight on you against Charlotte,which,as you've said her pokemon carries a lot of coverage,and Golem cannot hit hard,
Donphan is a lot better,if you can get Swampert it is even better,
Also Rhyperior is a lot more viable than Golem as a Stealth Rock user you can set Stealth Rock and then you can hit significantly harder with him,
And generally your team is very slow and need a lot of support,get rid of Ampharos,get a faster electric pokemon,such as Galvantula(also can set up sticky web) or Jolteon,
Your team has no wallbreaker reliable enough so,you have to change that,
You should have a stronger Psychic type,Gardevoir,Alakazam maybe Even Metagross,you can use Gardevoir as a support for your team,
Good luck ~