If you think about it, in great many fantasy stories, especially before the isekai boom, the life of the hero/heroine isn't exactly pleasant. It still shows in many shoujo/josei category isekai as well, where the MC is a villainess, although naturally in many cases she can completely remove the villainess status and live a good life. In many shounen/seinen isekai it's the life of a totally overpowered character, so not necessarily bad. But traditionally the main character of a story will face one challenge after another. In a minor portion of isekai it's still like that, all the way to fighting for basic survival time after time, or even getting tortured in edgelord stories. So, while it works in literature and makes a good read, who would actually want to live such a life? If you throw a real person into such a role, not to mention that without save/load they probably couldn't even do it, it could be a miserable life. It only works in literature. In real life, many would rather flee to the ends of the earth or even kill themselves to be free of it.
In the original novel being referred to in this series, Rebecca's life didn't sound pleasant. She must have suffered greatly and lost everything dear to her to want to destroy her own hometown. To achieve her revenge, she needed to keep playing three psychos in a careful dance of manipulation to make them wage a big war. What kind of life is that, anyway? No wonder she would deem it's not worth it and jump overboard.