Is she considered repentant after falsely accusing her friend, with her accusation remaining fresh in the minds of friends, despite her attempt to recant? And is she considered an oppressor if she cannot recant again after her friend exposed her and mentioned incorrect things about her character to her fiancé?

It is not permissible to slander a truthful woman or tarnish her reputation. One must hasten to repent to Allah and exonerate her from the falsehoods that were uttered. It is also not permissible for her to reciprocate with similar treatment or slander, for "Allah does not like the public utterance of evil, except by one who has been wronged." However, falsehood should not be met with falsehood. Disclosing a secret is betrayal and forbidden if it results in harm. One must repent to Allah, seek her forgiveness, and advise her to repent and forgive what transpired from her.