Disillusioned Cadence: Current story Idea (subject to change depending on circumstances.)
When the Canterlot wedding occurred, Cadence remained trapped in the catacombs due to her love being drained from her previously. Despite her weakness and sadness, she believed that the love she and Shining shared would break the Changeling queens spell and he would rescue her. She waited for years, as Chrysalis and her minions fed on her undying love and commitment. After a decade, the ruse was revealed when Sombra attacked Canterlot and Chrysalis was killed in the invasion.
Sombra and his forces broke in by traveling beneath the castle, through the catacombs. There, they ran into a unstable Cadence, who had been fighting off her captors after hearing the Shining was in danger. Sombra and Twilight killed the Changelings, thinking them to be guards. Twilight was about to kill Cadence but Sombra stopped her, fascinated by the mare's beauty, despite how clearly damaged she was. She thanked him and rushed to her would be husbands side, thinking he would break out of his trance as soon as he saw her.
Instead, Shining accused her of being a impostor and cast her aside, later dying in his attempt to protect Chrysalis and their child. Cadence was heart broken, left alone and looming over the body of her beloved as he embraced her captor lovingly in death. She would later take care of Chrysalis and Shining's child though it was less 'taking care of' and more just coldly looking on as the child grew. After the child was revealed to be changeling, it was only the fact that it was the child of her beloved that kept it alive despite all the hatred thrust upon it.