After reading for a while, I'm still not convinced that someone like Sigrid, who could blindly massacre innocent people, would have a change of heart this easily.
People's lives and ideals can change in a matter of days, sometimes even hours. It just depends on how strong the source of that change is - In Sigrid's case, she never bothered to think what she wants, she just followed rules others set for her because she thought that was her duty as a knight. Basically, she's the prime example that ignorance is NOT always bliss.
The first indicator of change was her death, obviously, and together with it came betrayal and disappointment. Everything she knew til then came crashing down, and the worst thing is, she didn't even understand WHY this happened to her.
The remaining indicators of change came gradually from her earnest wish to simply not die this time. She needed change, and she started from the basics. Sure, buying some new clothes and a house will not change her ideals (at all) but hearing her friends and colleagues talk about their own beliefs WILL make her think. All the people around her have reasons why they're doing what they're doing, or why they are the way they are, Sigrid just never bothered to understand these things. But now, it's like a new door opened for her, and she realized "hey, I am free to do whatever I want (more or less)", and that's enough to change someone by at least 90 degrees (since it takes a bit more for a full 180 degree change lol).
And her change is not even that fast, I mean we're at 30+ chapters and she only NOW realized she can be an Imperial knight and NOT support the Emperor lol. This girl is dense af, smh.