Goldenrodradio posted...OOOOH OH OOOOH.
Ok I thought it was the characters themselves that were weak against those types not their personas.
I'm dumb.
Their Personas define what they are weak to. Every character is bound to their Persona, EXCEPT the main character. So Chie is always going to be weak to fire, and Yosuke will always be weak to electricity.
To solve the issue with Chie, make a Persona who knows Red Wall, to give her a temporary resistance to Fire.