I'd say it's pretty well established at this point that, short of being informed in advance via spellbook, new spells are first learned of by way of accidental usage. Granted, Sarah knows she has a spell, but without context and experience, well, she's probably right.

I was thinking of having these thoughts in a later, less awkward moment, but that would imply Sarah's brain basically paused itself until after she finished getting cleaned up. That is not how showers work. If anything, they put brains into overdrive. Geniuses risk suddenly emerging and shouting "eureka!" while still covered in soap every time they shower.

In any case, we have our premise: Sarah trying to figure out on her own what spell she has, and her magic mark is a question mark. It's conceivable that Pandora may be something of a troll.