What could "touch the incongruous" mean? (from an old story)

The writer is juxtaposing the homely features of an ordinary woman— motherly, sedate, and wholesome woman,... prosaic domestic duties with the extraordinary gift she possesses— and yet seeing things— Probably, hence the incongruity. Why it should be to the point of alarm would possibly be understood fully from further context. Perhaps, people around her took liberties with her, made fun of her, and so forth; and the sudden epiphany or knowledge that she was more than just a factotum caused in these people a sense of alarm. But this is just guesswork.