Isn't that perfect position though?
No one expects anything from you, you still have all the luxury of being the daughter of a Duke and have the freedom to do whatever you want while having the mind of a 22 yo adult from a more developed civilization.
I know she is most likely retarted, since the MC of those stories are usually retarted in some way, but that is still the best possible situation.
I hated how they took so much time to stabilish the girl that don't matter anymore instead of talk about ou MC. Just indicates that it will be another that the reincarnation does not matter.