But Tiare Johnson would never under any circumstances have been rich. She could not keep money. The daughter of a native and an English sea-captain settled in Tahiti, when I knew her she was a woman of fifty, who looked older, and of enormous proportions. Tall and extremely stout, she would have been of imposing presence if the great good-nature of her face had not made it impossible for her to express anything but kindliness. Her arms were like legs of mutton, her breasts like giant cabbages; her face, broad and fleshy, gave you an impression of almost indecent nakedness, and vast chin succeeded to vast chin. I do not know how many of them there were. They fell away voluminously into the capaciousness of her bosom. She was dressed usually in a pink Mother Hubbard, and she wore all day long a large straw hat. But when she let down her hair, which she did now and then, for she was vain of it, you saw that it was long and dark and curly; and her eyes had remained young and vivacious. Her laughter was the most catching I ever heard; it would begin, a low peal in her throat, and would grow louder and louder till her whole vast body shook. She loved three things -- a joke, a glass of wine, and a handsome man. To have known her is a privilege.

请教老师：最后一句To have known her is a privilege.

为什么这里是To have known her is a privilege.，用不定式的完成时表达了什么含义？怎么理解？

根据故事的情节发展和上下文，这里为什么不是Having known her 或 Knowing her 呢？或是否可以To know her 呢？