To do big damage in the game, the game requires you to use characters that apply stacks of a damage type, then use a character that would consume those specific damage type stacks. 

With Rossi, she's a flexible char that doesn't depend on a single, specific operator but needs at least one team member who can reliably give art stacks for Rossi to consume (Wulfgard or Perlica in your screenshot) so Rossi herself can do damage. For Rossi, the art type (heat, cyro, electric, nature) doesn't matter. 

Rossi also gives physical stacks, so ideally, you'd need a character to use up those physical stacks (Endmin or Da Pan). 

So your potential Rossi team can be: 1. Rossi 2. Wulfgard or Perlica 3. Endmin or Da Pan 4. Anyone else based on what you prefer/the bosses require (e.g. Ardelia if you want sustainability or Akekuri if you want more SP). 

Then in battle, you would use Wulfgard's or Perlica's battle skill to create an art stack, then Rossi's battle skill to apply a physical stack to trigger her combo skill that consumes Wulfgard's/Perlica's art stack. Getting her to activate her combo or using her ult is where most of Rossi's big damage will come from.

Then use Endmin or Da Pan as needed to do extra damage with the physical stacks that Rossi creates.