I like how Sachi says it herself that she's just saying bullshit and should really be the one to apologize - she was looking to lash out, was looking to be angry and have a pinpoint target with good enough reason to be angry at, but when confronted by Punpun's genuine "I'm sorry," she's left with nothing to fight against...leaving her in her own pool of anger and self-misery, and realizing it all the way through. I think Sachi tries to be something better than what she actually is, tries to be this go-getter mangaka who pushes forward when really she's just as helpless as Punpun in this situation, no better and no different.