The child Ayesha Ali was found dead in her east London home with over 50 injuries.
The girl's mother, 35-year-old Polly Chowdhury, will now serve 10 years rather than 13 years in prison for manslaughter.
Her lover and co-defendant, 43-year-old Kiki Muddar, has had her sentence reduced from 18 years to 15 years for the crime by the Court of Appeal.
Sitting at the appeal court in central London today, the judges agreed that Muddar's sentence was "manifestly excessive" before reducing it by three years.
Muddar had created a cyber-fantasy world to manipulate Chowdhury through a series of fictitious friends on social media.
"She was rational in her judgments in having a disgust with Ayesha. She did not likeChowdhury putting Ayesha above her interests. However immoral, abhorrent and illegal her judgment, it was rational... There is no question of either defendant having been mad,"prosecutor Richard Whittam had told the court during their trial earlier this year.
Muddar befriended Chowdhury when they lived next door to each other and she got sympathy by pretending she had cancer.She even blamed Ayesha for making her fictional cancer worse.
Post-mortem examinations showed Ali died as a result of damage to the head from a blow or blows.
The reduced sentences were not intended to undermine the gravity of the crimes. The judge said Ali "did not deserve to die as she did" and it was proper that the women should serve what remained lengthy prison sentences.
