As with her heat swim this morning, the 17-year-old produced a blistering freestyle leg to win in 3:05.39, dipping 0.75 seconds inside the mark she had set this morning.
The Swansea-based swimmer had been shocked by her earlier performance today and on seeing the scoreboard tonight, she had a beaming smile on her face.
It was her second title of the week after her success in the 400m Freestyle - S6, also in a world record time.
She said: 'Personally, I believed I was going to get that gold medal. Tonight, I knew I was on form from this morning. I knew it was going to be tough, but mainly I was racing against myself. I knew there was going to be people out there to watch.'
China's Xu Qing cut an astonishing 3.37 seconds off Sascha Kindred's world record to win the men's 200m Individual Medley - S6 race.
The Briton had not been dislodged from the top of the podium since first claiming gold in Sydney 12 years ago and was fourth at halfway before his breaststroke leg pulled him up to second, narrowly behind Xu.
It looked as though it would be a stroke for stroke duel but the Chinese swimmer pulled away to touch in 2:38.62.
China's Yang Yang set a new world record of 2:03.71 in the men's 100m Freestyle - S2, while compatriot Yang Bozun triumphed in world record time of 1:10.11 in the 100m Breaststroke - SB11 and Ihar Boki's 56.97 was an 100m Backstroke - S13 record.
Denis Tarasov of Russia lowered his own 50m Freestyle - S8 mark to 25.82, Pan Shiyun won the 100m Freestyle - S7, Maksym Veraksa the 200m Individual Medley - SM12 and Michael Schoenmaker of Netherlands won the 100m Breaststroke- SB3.
Xia Jiangbo set a new world record of 1:44.32 in the women's 100m Freestyle - S3 with Maja Reichard's 1:27.98 a new 100m Breaststroke - SB11 mark.
Russian Oxana Savchenko dipped almost two seconds inside the 200m Individual Medley - SM12 mark in 2:28.00, Australia set a new mark of 4:20.39 in the 4 x 100m Freestyle Relay - 34 Points and Jacqueline Freney won the 100m Freestyle - S7.