Zainab al Hilli was shot and so brutally beaten during the attack that doctors placed her in a medically-induced coma.
She has since regained consciousness and was able to hold a brief discussion with officers in France, sources close to the inquiry have said.
Zainab is seen as a key witness to the horrific attack that left her parents and grandmother dead.
Saad al Hilli, 50, was killed in the family car alongside his dentist wife Iqbal on Wednesday in a remote spot close to Lake Annecy.
Mrs al Hilli's mother also died in the shooting along with Sylvain Mollier, 45, a French cyclist who apparently stumbled across the shooting.
Zainab's younger sister Zeena, four, who survived by cowering behind her mother, has flown back to Britain.
While she is unable to shed much light on the murders, French police believe Zainab could provide them with crucial details to help piece together what happened.
A source said: "They have been able to speak to her but this was just an initial meeting. They could not go into any detail and the child was very tired. It was not permitted for the discussion to go any further."
Police must now wait for a green light from medics before they can engage the girl in a more lengthy discussion.
Her sister Zeena returned to Britain after two relatives, understood to be an aunt and uncle, flew out to France. She is under the care of the authorities and social services.
The spotlight in the criminal inquiry has turned on the al Hilli family home in the affluent village of Claygate in Surrey after police identified items of concern and called in a bomb disposal squad.
Neighbouring properties were evacuated as experts examined the mock-Tudor house, focusing on a shed at the bottom of the garden. But officers later said that the unidentified items were not hazardous.
As attention on the family home intensified, it emerged the four shooting victims were killed with the same gun, fuelling speculation they were targeted by a highly-trained contract killer.
French police are also examining two mobile phones found in the al Hillis' bullet-ridden BMW, just a few miles from Le Solitaire du Lac, a campsite in Saint-Jorioz where they were staying.