Please teach me what these sentences mean

Question

It wasn’t that she looked as if you could have given her shillings—it was impossible to look less so. Yet when she finally drifted toward him, distinctly handsome, though ever so much older—older than when he had seen her before—it might have been as an effect of her guessing that he had, within the couple of hours, devoted more imagination to her than to all the others put together, and had thereby penetrated to a kind of truth that the others were too stupid for. (https://www.gutenberg.org/files/1093/1093-h/1093-h.htm)

The sentences above are quoted from the second paragraph on chapter.1 of "The beast in the jungle" by Henry James. Then I have three questions.

1. What does "she looked as if you could have given her shillings" mean? Is shillings in the sentence something like tips?
2. Does "it was impossible to look less so?" mean more or less "it looked so"?
3. What does "it might have been" mean?

(The three points that I am asking about are emphasized.)

I would appreciate it if you would answer my very long question. Because this story is intriguing, I really want to understand.

Answer 1

It seems that May is a long-term guest in a large, historic house. In those days such houses were not 'open to the public' in the way that they are now, with large numbers of people lining up to buy tickets - but groups of visitors might sometimes be shown round by a senior servant or, in this case, a 'poor relation'. May does not look at all like a servant, the sort of person who might get a shilling tip for acting as guide. (A shilling was a pre-decimal British coin, equivalent to 5p but worth much more 120 years ago.)

The reason for her 'drifting towards' the protagonist might have been because she guessed that he had been thinking about her.