Trishna is already doing well enough that she could leave intensive care, said Wirginia Maixner, director of neurosurgery at Royal Children's Hospital.
"She looks brilliant, she is talking, she is being Trishna, she is behaving the way she always has," Maixner told reporters. "She's phenomenally good."
Her sister, Krishna, will be slowly brought out of the coma later Thursday, Maixner said. Krishna will have a longer period of adjustment as the separation brought more changes to her body and brain's blood circulation.
Maixner said they hoped to have an indication Thursday night or early Friday about how Krishna's brain was responding. MRI scans Wednesday showed no signs of brain injury.
Maixner said there may be minor changes to the girls from where their brains were separated but that overall the brains looked good.
"I can tell you that it's not until I saw that scan that I had my first breath of relief," she said, revealing she did a short "chicken dance" when she saw the positive images. "The scans look great. I believe we've brought them through safely. I believe that the girls will come out really, really good."
The twins, who turn 3 next month, had been joined at the top of their heads and shared brain tissue and blood vessels. They were separated Tuesday after 25 hours of delicate surgery, and then underwent an additional six hours of reconstructive work.
Maixner said after the girls have recovered, their next hurdle will be learning to walk.
"There will be a process before the girls start walking and they have gone through so much in the last two years that it will take a bit of time - but they will get there," she said.
Doctors had earlier said there was a 50-50 chance that one of the girls could suffer brain damage from the complicated separation.
An aid worker first saw Trishna and Krishna in a Bangladeshi orphanage in 2007 when they were only a month old, and arranged for them to be brought to Australia.