More CCTV footage showed Porton stopping for petrol on the way to the hospital even though her daughter was dead in the back seat.
Then, just three weeks later on February 1, little Scarlett was also suffocated by her mum.
The court was told that Scarlett had been dead for hours before Porton called for help. When she was asked if her daughter was breathing, Porton replied 'no'.
Both girl's deaths were consistent with deliberate airway obstruction. Prosecutors said doctors 'could not find any natural reason why either, let alone both, should have died.'
Evidence showed that Porton had tried to kill Lexi twice in the lead up to her death. Lexi was taken to hospital on January 2 and then January 4, but was sent home with antibiotics for an apparent chest infection.
While there, Porton, who worked as a part-time model and sex worker, went into the hospital toilets and took topless photos of herself and arranged to perform sex acts for money with a man she had met through a website
The day after Lexi's death, Porton accepted 41 friend requests on the dating app Meet Me and was also messaging men on another app, Badoo.
'My little girl passed away yesterday,' she said to a man named Dave, before replying 'its alrite' to his condolences.
In the lead up to the death Porton searched 'can you actually die if you have a blocked nose and cover your mouth with tape' online and paramedics described her as 'calm and emotionless' when they arrived to treat Scarlett.
During the trial Porton's landlady described how she spent 'more and more time' caring for Lexi and Scarlett while their mum was 'doing social things' instead of looking after them. In a statement to police she said Porton was doing 'whatever she could not to have them with her'.
Detective Superintendent Pete Hill, of Warwickshire Police, said after the case: 'She (Porton) has lied repeatedly to friends, family and professionals to cover her tracks. At no point throughout the whole investigation has she ever shown any real signs of emotion.
'Our thoughts are with the families of Lexi and Scarlett. I'm sure today's outcome will do little to heal their pain, but I hope they can take some comfort.'
The girls' father, Chris Draper, said the 'only comfort is that Lexi and Scarlett are together.'
Porton will be sentenced by Mrs Justice Yip on Friday.