Mara laments the state of the Dreaming City and its curse, laying the blame for it at Riven's feet.
The scrolls we recovered from Savathûn's Spire confirmed her greatest fear: the curse is unbreakable. Once granted, an Ahamkara's wish cannot be undone.
Mara dislikes Riven's bargain, but knows we have no other option. She tells us to cooperate with Riven for now while she thinks of a contingency plan.