Franziska's suspicion of Onerion stems from the fact that it is his monsters that are racing away at 6pm, and that he is absent from dinner. She hasn't really interacted with the spider at all so she doesn't know too much about all that...

That being said, Franziska will totally storm up to Onerion and ask him what is going on and what's this about spiders, using her best barbarian Intimidation!!

If this requires another roll I'm happy with any DC.