A teenager who vanished after taking out the rubbish was upset because her family's asylum-seeker status barred her from attending university.
Nida Ul-Naseer, 18, of Newport, South Wales, has not been seen since stepping outside her home in Linton Street on December 28.
Her family revealed today that their attempt to seek asylum in the UK from Pakistan was turned down a year ago.
It meant that academically-gifted Nida opted to retake a business studies course she had already passed.
Her sister, Shamyla, 23, told a press conference today that she believed Nida's disappearance stemmed from being upset because she could not attend university.
"I think that not being able to go to university is the reason for her leaving," she said, speaking alongside other family members at Newport Central police station.
She said her sister had been upset and angry about the situation before she vanished.
Nida might also have been barefoot when she disappeared three days after Christmas, it has emerged.
Police said it was not known if she had taken anything to put on her feet, although if she had planned to leave it was likely.
The teenager suffers from a medical condition and needs medication without which she is likely to become anaemic.
Her sister revealed today that Nida had been taking iron supplements and also suffered from heartburn.
The teenager had been unhappy for some time about not being able to attend university.
Her sister said she had seen friends who did less well in their exams go on to university. She went to college instead but remained unhappy.
Before she left she had argued with her family about her inability to go to university and was "shouting and crying".
Her father, Naseer Tahir, who was also at the press conference, said in broken English that he was happy for his daughter to attend university.
He added that he was sad he was not able to provide her with what she wanted.
The conference heard that Nida did not have a boyfriend and was described by her family as "very religious".
The family have been seeking asylum in the UK for five years. Their passports are held by the Home Office.
Sister Shamyla began the interview with a direct appeal to her missing sister, saying: "Nida, please come back home.
"Nida, please come back home. We are desperately worried about you. Nida, we need you. Nida, please come back home, we cannot live without you."
The family's plea to Nida came as the police also made a direct appeal to the teenager during the press conference.
Superintendent Mark Warrender said: "Nida, if you are watching or listening to this please, please get in touch. Your family is desperately worried about you and all they want to know, and we want to know, is that you are safe and well."
He also gave an update on the progress of the investigation, but acknowledged that there had been no sightings of Nida since she left home.
Mr Warrender said forensic examination of the teenager's mobile phone, to which she was addicted, and other electronic devices was ongoing.
Officers are also sifting through hundreds of hours of CCTV footage taken from the area to see whether they recorded any of her movements.
He said investigators were keeping an open mind with regard to Nida's disappearance and all and any lines of inquiry would be followed up.
"We are keeping an open mind but it really is a mystery."
Mr Warrender said that since she left to take out the rubbish at 8pm on December 28 "we have no confirmed sightings".
With regard to whether the teenager was barefoot when she left, he said: "It is the belief of the family that when she left she may have been without her shoes."
He added: "It may be that if she planned to leave she may have had something to put on her feet."