She has no recollection of the incident but suffered a cardiac arrest and had to be resuscitated.
A year later, she is in wheelchair and has severe physical difficulties as well as brain damage which has led to emotional and cognitive problems.
In the ear where she was holding the phone, she has a burst eardrum and persistent hearing loss.
When a person is hit by lightning, the high resistance of human skin causes the lightning charge to flows over the body - often known as an 'external flashover'.
But some of the current can flow through the body. The more that flows through, the more internal damage it causes.
Conductive materials in direct contact with the skin such as liquid or metal objects increases the risk that the current will flow through the body and therefore cause internal injury.
Rare occurrence
The doctors at Northwick Park Hospital in London who treated the girl's hearing injuries found three other cases of people being hit by lightning while talking on a mobile phone - all of whom died of their injuries - in China, Korea and Malaysia.
They said although cases were rare it was a public health issue and people needed to understand the risks.
Swinda Esprit, a doctor in the ear, nose and throat department said: "It is obvious really but we all carry mobile phones and we don't think about it.
"If you're struck by lightning on its own it will flash over your body but if you're holding a phone it will internalise and cause much worse injuries.
"Children particularly won't realise the risk.
"In Australia they have guidelines, and one of the things they say is not to hold mobile phones outside during storms."
Dr Esprit said mobile phone manufacturers should warn consumers of the dangers.
Paul Taylor, a scientist at the Met Office said it could also be dangerous to carry a mobile in your pocket during a storm.
"It is well known within the thunderstorm detection community that wearing or carrying metallic objects can increase the likelihood of injury.
"It certainly adds to the intensity of the skin damage and the article certainly amplifies that here.
"I would treat a mobile phone as yet another piece of metal that people tend to carry on their persons like coins and rings"
