Superficially it is a really cute and touching chapter, but what if it is all a trick from U-Ran to make Six lower his guard in order to do whatever she wants without him trying to stop her? after all her Bewustein system is more advanced so it stand to reason that she has the ability to lie and deceive, plus even in this chapter most of her interactions come from a self-centred sense of superiority.
@Kaiser92 there are 2 problems with that, she is not a human, and she is not killing humans, she it not even destroying robots that can feel (which was her argument), also that answer doesn't solves the question of why she shouldn't destroy the other robots regardless of how advanced they may be, also the people financing her construction want her to be a brawling robot that will end destroying other robots for entertainment which while running contrary to the "lesson" of this chapter doesn't contradicts the answer at quora.com
@Nolonar And this chapter doesn't answer the question either, she just came around to feel bad because the only one she could talk to started ignoring her, but Six never gave her an answer, matter of fact his answer was that he didn't had one and thus couldn't no longer be her big brother.
So i assume that U-Ran at one point somehow realised that what she did was bad because she trampled on the hard-work of others which is why Six became angry at her, but i don't think she has come to that point yet, because it also means that she now can appreciate the work of others even if they are less advanced than herself (i don't think she has developed true empathy yet), and Six himself didn't explained that to her neither, so even in the case that she is feeling bad i think that rather than guilt she is just feeling lonely and hasn't actually learnt anything, however i personally think she is acting and she is not actually feeling lonely at all.
The thing with the Bewustein System is that it is so advanced that the 3 possibilities remain, but i am not sold on U-Ran having learn something out of nowhere that Six never explained to her, so that leaves her just feeling lonely or acting it out for further gains.