Okay, we've seen Susan's boots while dressed like this. She can have a proper outfit again.
...What? That's not a weird thing to say.
I found the concept of Susan not being able to explain the potions while using the "drink this" expression, and it just being her saying the same thing while gesturing in the same way to every NPC, a difficult one to get across, so we wound up with a panel that just really hammers home that there's simply no explaining it to the generic NPCs.
Well, that, or they know exactly what's up and are just being weird about it. Either way, the game has decided this is all quite evil.