As if the lady of a well off, important noble house would be going around teaching other people's children, like she was wanting for money. It would be a disgrace. Just dispensing some information/advice, of course, would be a different thing. Though she should be careful not to pretend too much. It would be better to try to convince them of the simple truth that Lippe just is smart. It's not like her both sons would be so calm and collected.