Read the following passage carefully.

she was such a sharp little lady, and used to sit with her hands folded in each other, looking so very watchful while she talked to me that perhaps i found that rather irksome. or perhaps it was her being so upright and trim; though i don't think it was that, because i thought that quaintly pleasant. nor can it have been the general expression of her face, which was very sparkling and pretty for an old lady. i don't know what it was. or at least if i do, now, i thought i did not then. or at least—but it don't matter.
(from bleak house, chapter xxx, by charles dickens)
how do the last three sentences contribute to the passage?

they to characterize the narrator as someone too kind and shy to admit that she disliked someone.
they add valuable details to the plot.
they characterize the old lady as someone unkind and unfair.
they have no value at all.