Coroner John Gittens said: "She could hear Mia singing and talking in the bath next door.
"She shouted Mia's name to confirm she was there. Then a pink brush she had been playing with banged on the side of the bath.
"She ran in and found her lying face down in the water. She lifted her out. She was pink and floppy and not breathing."
The inquest was told Eastham-Jones pulled Mia out of the bath and began CPR immediately.
An ambulance was called and she was taken to hospital but despite being given oxygen and adrenalin, she died the next morning.
A post-mortem concluded Mia had suffered multiple organ failure, including damage to the brain, kidneys and heart.
The death was ruled an accident.
Gittens said the incident, which happened last January, was "tragic" and offered condolences to the family.
"She was left for a very, very short time by her mother in the bath, and sadly the circumstances which occurred thereafter were those which resulted in her passing.
"I would like to record my very sincere condolences to the family of Mia in her tragic loss."