So basically the mc (female) is experimented on and is turned into a literal sword where she is super powerful but is used to fight wars for many centuries. Somehow she is reincarnated to the time before she was transformed into a sword.
Sounds like:The taming of the tyrant
https://www.mangago.zone/read-manga/i_tamed_a_tyrant_and_ran_away/
I Tamed a Tyrant and Ran Away
So basically the mc (female) is experimented on and is turned into a literal sword where she is super powerful but is used to fight wars for many centuries. Somehow she is reincarnated to the time before she was transformed into a sword.