Heartfelt Regrets, Love in Liyue

The heroine has cancer and only three months to live. During the first two months, she and her best friend take revenge on those who hurt her. In the final month, her friend stays by her side as she slowly slips away.

Angst + partial revenge + the world's best best friend + heroine with cancer + three months to live + heroine dies + the true heiress of a wealthy family, ignored by her relatives + everyone protects the fake heiress + the others finally realize their mistakes after the heroine dies + the heroine's best friend reveals the whole truth in public, then follows her in death