Sentimental Education: Rosanette

Throughout most of the novel, Rosanette's been described as a pretty but shallow, ignorant and frivolous girl. She has several lovers, likes fancy things, knows nothing about politics and arts, advocates the idea of women being at home, etc. Flaubert stays strictly as a spectator and never enters her mind.
Then in 1 scene in part 3 chapter 1, while looking at a little girl and getting lost in thoughts, Rosanette gives a deep sigh and starts talking about her sad childhood, but, perhaps pained by memories, leaves the story unfinished "Oh, let's forget about it!... I love you, and I'm happy. Kiss me."

"Frédéric was thinking above all of what she had left unsaid. By what steps had she succeeded in emerging from poverty? What lover had given her education? What sort of life had she led up to the day when he had 1st been to her house? Her last admission forbade any further questions."

They change topic, and again leave things unsaid.

"For in the midst of the most intimate confidences, false shame, delicacy, or pity always impose a certain reticence. We come across precipices or morasses, in ourselves or in the other person, which bring us to a halt; in any case, we feel that we would not be understood; it is difficult to express anything at all with any degree of exactness, so that complete relationships are few and far between."

She has never known anything better than this. "Often, as she gazed at Frédéric, tears came into her eyes..." Then why has she resisted him so long? He asks. She, clasping him in her arms, answers:
"It was because I was afraid of loving you too much, darling."
As the scene ends, we hardly know more about what she has been through and what has shaped her as she is, and we never, even once, know what goes on in her mind, but having got a glimpse of her hidden tragic side, a glimpse of what lies underneath that spoilt, superficial image, we can no longer perceive her the same way. 
And we ask ourselves: What do we know about the people around us?