Cersei accuses Unella of not truly caring about Cersei's atonement when Cersei was imprisoned by the Faith Militant; rather, Unella tortured Cersei solely for her own sick satisfaction.
See it all on demand.
She then recalls that despite being enemies in the series, Lena Headey was not comfortable with the way that turned things.
After the Red Keep is destroyed by via dragonfire during the , Unella's fate remains unknown, though it is very unlikely that she survived its destruction.