At this point Mrs Gould has not yet realized the extent to which Charles has sublimated his feelings to his rational calculation. The extremity of her surprise (she is literally wide-eyed) is due to the notion, striking her at this moment, that he is one with the visiting capitalists, i.e., a pure materialist with no sympathetic feeling to match her own.

Another interpretation, by no means at odds with the first, is that Emily's "expressively" lowered eyes were meant as an invitation to more than discussion, and that her surprise is due to another kind of "silence" on Charles' part.