Not... Really...? I don't really see what you mean, yeah she changed but that's normal, she's growing as a person and it wasn't so sudden, it would be shocking...(And we can't really count the times where she acted on purpose so...)
growing as a person, sure, but when she expressed that she was literally raised to be a military murder machine with little comfort in her life, and then she’s transmigrated into a place where she’s sucked into the madness of war again, it’s just a bit strange to see her glow with joy so suddenly. i totally get your point though, she did grow as a person throughout her time in the new world, but it’s just a bit shocking imo that after an entire life of still emotions, she was able to adapt so easily, if that makes sense? and we don’t really get to she too much narration from her so yeah it’s hard to tell at which point she may have been faking it, but it looked genuine to me so i always just assumed lol.
I see where you're getting at, when there is reincarnation, I always assume that a little part of their personality is gone since you know, it's an entirely new body and so the sequels of her tough training and torture before are gone. And also because the previous owner of the body easily smiled, at least much more than Kaisa before, so it would explain how she has more ease faking it.
And yeah I think that some of the personality of a person is affected by her body, by how they perceive themselves although it may seem weird, maybe...
Maybe it might be the fact that she has had to bottle up all the positive emotions inside of her due to the environment before but now in this world she has a lot of people who wish for her to live and be happy, so now that she can let go a little bit they are all flooding out
wow her personality and energy has changed so much it’s strange