Faolyn
(she/her)
Zariel, IIRC, was corrupted from what was likely thousands of year's worth of evil emanations from her time fighting in Hell (i.e., not a lot of free will involved here), and from what I can tell, Fall-From-Grace suffered thousands of years of torture by devils, which probably had something to do with her change of mind.I'm not sure that is entirely supported. Zariel is listed as a fiend, but was created as a celestial. If it is possible for a celestial to fall and become a fiend, it implies it is also possible for a fiend to rise and become a celestial.
Not 5e, but there is also the character Fall-From-Grace in Planescape: Torment, a lawful neutral succubus.