Agatha doesn't like how familiar this foreign boy appears to be with Bertie. He's likely had some terrible influence on her nephew that she has yet to gauge. Comrades-at-arms should have gone their separate ways after the war.

"If this war of yours is over now that you're here, then why are you imposing on my nephew still? Don't you have one of your own little hills the kidnappers brought you to?" Clearly, this is going to be a sticking point for her. "Surely you can manage something on your own." She huffs, but it is annoyed. "And if Jeeves isn't here, then who's keeping this house clean? It's certainly not Bertie. He can't have changed that much." Perhaps the boy is Bertie's servant without really noticing. He's foreign. They're foolish enough to assume that kind of arrangement is normal, probably.