Making him look unreasonable for refusing to work with her when she's not up to anything could in fact be what she's up to here. There's not really anything else he can imagine she gains from this.

"You can come, if you like."

"We are all of us inspired by your mercy and your generosity towards your defeated enemies. I will come, then."

Oh, good. That means they'll likely pull everything off without any kind of trouble.

Joan-Pau Ardiaca considered charming an urchin and decided it might blow the whole operation, which is really the fundamental problem with all of her suggestions - that trying to do what she just tried might have blown the entire operation. She succeeded, obviously, but while that might be evidence she's smart enough to get away with doing this on a regular basis it's not proof.

You just edit their memories if they're suspicious of you, it's fine. 

You mean with the obvious permanent-duration spell one dispel will take care of? Because whether you do or don't doesn't matter when your entire plan revolves around nobody watching while you do something.

No, with one of the many spells that works better than that. The kids these days. No memory-editing finesse whatsoever.

Maybe if anyone other than you and your secret evil archmage mother knew about those you might be believed to be mildly more competent than you are currently believed to be!

Lilia has never run into problems caused by people assuming she is incompetent - usually it's to her advantage - and would be unmoved by this, were the entire dialogue not in a hypothetical anyway.