This is actually pretty nice. The MC initially understandably strongly rejects her reincarnation, cause of course you would if you had a happy life and died so suddenly. The chapter where she reconciled with those feelings actually made me a little sad, though, she did kind of go from "hell no" to "fine, okay" in like a chapter. Still, there's nice buildup to that I suppose.
One thing I am slightly worried about is how they are going to deal with her mental vs physical age. She jumps between acting like a child and internally thinking like an adult. It makes it a little confusing which the author intended to make her act as. Just one line being like "I know I'm actually 25 now, but children only get to act like children for a few years, so I'm gonna do that" could help. I know I'd take advantage of having immature and selfish behavior being waved off. And of course, romance. I know that it will be between her and the prince. I really hope it doesn't happen. At least until they are in their twenties. She seems to be crushing on older men right now and it's not like she can do anything as a 5 year old, so at least she isn't being weird about it now.