I've been following her work for a long time and now that I read this comic... it was really confusing. Especially the nihilistic part was really creepy. I'm an atheist and I don't need God to tell me what is morally right or wrong.
The comic comes off strongly as someone dealing with some form of mental illness/es.
The panic over the heat death of the universe could be anxiety or even a form of OCD. I am not trying to diagnose her but I do feel confident saying she would benefit from a licensed mental health professional.
The "nihilist" stuff sounded a lot like intrusive thoughts. Intrusive thoughts are a part of many mental health issues and can be incredibly distressing.
In an extreme example - there is a form of OCD that causes someone to be panicked that they may be a child molester. This person has
never harmed a child, actively avoids children to avoid harming them, and is not likely to ever actually harm a child. (When it is this condition) But their intrusive thoughts are so strong the person is genuinely terrified that they will harm children.
So the "nihilism" that Minna describes sounds a lot like that. It doesn't seem that she actually acted on it in a serious way. Yet she still saw herself as so "nihilistic" from these thoughts.
Getting schadenfreude from seeing other people suffer - it's documented, you can get a dopamine hit from seeing a bad thing happen to someone else. When you're struggling with failing mental health, which can reduce joy from healthy areas, this dopamine hit can feel really good and then you seek it out. It's not
great - but just getting pleasure from seeing others' bad news doesn't innately do harm, but plays into the intrusive thoughts that she's a bad person.
So, in conclusion - while I cannot say exactly what was going on, what Minna expressed in the comic strongly matches a person going through a mental health crisis without proper treatment.