Canonically we know that Cass pictures what Steph would tell her in those dire moments where she needs to make sense of her emotions
But what if she pictures Steph in those not-so-dire moments too. Like Steph is just the stopper in all her impulsive thoughts
Cass: *sniffs a bath bomb*
Cass: Ooh. Smells like cupcakes.
Steph's voice in her head: Don't.
Cass: *lifts it to her mouth*
Steph with a metaphorical spray bottle: No! Bad girl! Put that down!
Cass, pouting: Fine.