This is not a story about the Doctor but the Rani
It is a story of redemption, a story about a woman once considered amoral finding herself and connecting with her own emotions
She chooses to take only a female companion because her observation of the Doctor and his life has shown a greater degree of success with female humans than males of that species
I am the Rani and I shall need your aid in connecting with my feelings, your opinion of when I am being callous or cold to the suffering of lesser beings
For your aid I will if you wish genetically alter you to live a longer life than is common in humanity, immune to diseases and many poisons, or I could leave your DNA intact your choice.