The conjoined twin Jodie was in a critical but stable condition last night after a 20-hour operation that ended in the death of her weaker sister, Mary.

The conjoined twin Jodie was in a critical but stable condition last night after a 20-hour operation that ended in the death of her weaker sister, Mary.

A medical expert said the next 48 hours would be crucial for Jodie, who was recovering in the intensive care unit of St Mary's Hospital, Manchester. Professor Lewis Spitz, a paediatric surgeon at Great Ormond Street Hospital, London, said she would need "minute-by-minute" monitoring.

After the extraordinary human drama in which Mary paid with her life to save Jodie, Professor Spitz suggested that a mirror placed beside Jodie could help to lessen the stress of losing her sister.

Use of a mirror was one of several "little tricks" that could improve Jodie's chances of survival in the next few days, he said. Professor Spitz has not been involved directly in the case of Jodie and Mary but has treated 17 sets of conjoined twins since 1985.

He said: "These babies are extremely critical after surgery and they have to be carefully monitored in intensive care. They are very unstable, requiring meticulous attention...

"A huge body mass has been taken from them of between at least 45 to 50 per cent. The heart has been used to pumping blood through a huge body mass, which has now been reduced, and intensive care and careful monitoring is critical."

He added: "The process is by no means over. The intensive care... will continue for the next couple of days and maybe into the next couple of weeks before she is out of the woods."

St Mary's hospital said Jodie was "critical, but stable", while Mary, who had no functioning heart or lungs, had "sadly died". A spokeswoman said the surgeons were "exhausted and in bed".

Details of the operation have not been revealed. The hospital said it had no plans to hold a press conference "in the foreseeable future" owing to the terms of a court injunction that prevents information about the case being released.

The injunction was imposed at the request of the parents, who are Roman Catholics with strong religious convictions from the Maltese island of Gozo, but could be lifted if, as reported, they choose to sell their story to a TV programme to raise money for Jodie's care. The parents, who were initially opposed to the separation and triggered a series of court hearings, were present at the hospital throughout the operation and were kept regularly informed of progress.

The operation on Jodie and Mary, at 20 hours, had lasted longer than any done at Great Ormond Street on conjoined twins. The longest operation Professor Spitz had undertaken lasted 17 hours on Irish twins, one of whom died three days after surgery.

On Jodie's chances of having a good quality of life, Professor Spitz said: "It would depend on the function of her bladder and bowels and lower limbs. It could range from a very good... where she can walk and function normally, to the other extreme of not being able to walk and being incontinent."

He added that if he were in charge of the case, he would want to introduce Jodie's parents to conjoined twins who had survived separation to show them how successful the operation could be.

Great Ormond Street has a survival rate of about 80 per cent. Of the five sets of conjoined twins Professor Spitz and his team have separated since 1985, eight children are alive and two are dead.