The opportunity to prevent someone from embarrassing themselves in front of the other people they'll see that day is also an opportunity to feel a little awkward yourself. The Princess feels that awkwardness is excruciating and so not as funny as Michael Cera would have us believe. In fact, she has avoided these kinds of opportunities so frequently that now it rarely even occurs to her to say anything at all. For example, if she is eating dinner with a friend, and that person has huge chunk of spinach in his or her teeth, the Princess doesn't say anything. She just stares at the spinach. Later, that person is all, yikes there's spinach in my teeth, why didn't you say anything, and the Princess is like, um, I just didn't think about it.
But she actually thought about saying something to the toilet paper girl. She even turned around twice after deciding not to tell her, and each time decided again not to tell her. It's so unfortunate.