I'm going to be conjecturing in the dark here, but I think that Marianne has good sense as in good instincts, leading her often right (at least in the past). She definately acts on impulse without thinking things through first, but most of the time the feelings have good or well intentioned origins - did perhaps lead her to the correct surmises.

I think that is also Marianne's argument in life - she feels that one should be guided by good instincts alone and that one should act out of your nature - no editing allowed as Elinor does, who follows the counter argument that although feelings can guide you, they cannot always be trusted and must be investigated well first. For Marianne what you see is what you get - to her it is not even a possibility that someone could appear to be one thing and be another.