The girl's father told the BBC that they feared she would bring dishonour on their family. Her mother said it was her "destiny" to die that way. She hadn't brought dishonour on the family, yet - this was a preventative murder, just in case.
The couple were arrested in Pakistani-administered Kashmir last week.
The Human Rights Commission of Pakistan reported 943 women died in so-called honour killings last year. Those are just the ones they know about.
That represented an increase of more than 100 from 2010.
Police say that the incident took place in a remote village in the southern district of Kotli. They say that the case was brought to their attention by the couple's eldest daughter.
The girl, known only as Anusha, was found to have burns over 60% of her body. Her father Muhammad Zafar told the BBC what happened:
"There was a boy who came by on a motorcycle. She (Anusha) turned to look at him twice. I told her before not to do that, it's wrong. People talk about us because our older daughter was the same way," he said. So, if people didn't talk about them, they wouldn't have tortured their daughter to death? They murdered her to impress the neighbours!!!
Her mother Zaheen described the aftermath: "She said 'I didn't do it on purpose. I won't look again.' By then I had already thrown the acid. It was her destiny to die this way."
And you know that because that's the way she died?
Anusha's father is reported to have taken his daughter inside, beaten her and then acid was poured over her with the help of his wife. Officials say that the couple did not take their daughter to hospital until the following morning. This is just unbelievable! How do they justify that? It's impossible. They are not even human.
The couple say that an older daughter had already disgraced the family and they did not want to be dishonoured again. So pouring acid on a daughter who hadn't yet done anything disgraceful somehow restores honour? How utterly absurd, if not outright insane!
Police say this is one of the first cases of its kind in Pakistani-administered Kashmir, where such killings are relatively rare.
In March the government of Pakistani-administered Kashmir made acid attacks a criminal offence punishable with life imprisonment. And yet... I hope Mr Zafar enjoys his 'honour' while rotting in jail for the rest of his life, and then rotting in Hell after.