@justforthelulz
It's been a while since I've had a chemistry class, but I think that rather than a level of acidity, it depends on the type acid. It needs to be some acid that reacts with silver to form a compound that's liquid at the soup's temperature or something that could be soluble in...
@broadsword80
It's not that serious. If you check the first chapter of the main series she just wanders into their garden and like sits down hungry. Then she gets fed and hired.