Xynthia Hawke was 28 and expecting her first child, with all the excitement and delight of a new mother to be. She and her French partner, Yannick Balthazar, had planned everything down to the last detail in what they hoped would be as natural a birth as possible in a specially chosen clinic.

“Xynthia liked to be prepared for things and this was just the most exciting thing ever to prepare for,” says her sister, Iris Hawke. “She sailed through the pregnancy; she had none of the sickness, just the good things and lots of mental clarity. She was swimming, doing yoga and eating well and she and Yannick were very happy. They had bought a new house and had everything ready for the baby. It was all perfect.”

Neither Balthazar nor the Hawke family could have prepared for the tragic events that followed when doctors at the private maternity clinic in Orthez, south-west France, decided an urgent caesarean section was needed.

On 26 September 2014, Isaac was born healthy, but Hawke would never get to hold him. She lay in a coma from which she would not recover after an alcoholic anaesthetist, reportedly found to be three times over the legal drink-driving limit, botched the procedure.

The Belgian doctor, Helga Wauters, 51, is facing trial for manslaughter after allegedly placing a breathing tube into Hawke’s oesophagus instead of her windpipe. Starved of oxygen, Hawke had a heart attack, went into a coma and died four days later.

Iris Hawke still has difficulty recounting the entirely avoidable event that caused her sister’s death. She refers to it as le truc – the thing. “My sister’s life was put into the hands of an anaesthetist who was in no fit state to be working in a hospital or be in control of anyone’s life,” she says.

Speaking for the first time, exactly four years on, Iris told the Guardian how the lives of all those who loved and knew her sister had been shattered. “For a long time I wasn’t able to think about what happened that night. It was too difficult. Even now, it’s hard.

“I remember my dad calling me and it must have been around 5am. Nobody phones at 5am so I knew something was wrong. He said Xynthia had had the baby and the baby was fine, but Xynthia wasn’t. It was horrible. He said I should get a flight at once. When I arrived Xynthia was in a coma in intensive care. They couldn’t do anything for her. It was a terrible, terrible time.”

On 30 September, Xynthia Hawke died. She never saw her baby.

Iris Hawke says that, growing up in Somerset, she and Xynthia – “the girls” – and their parents, Fraser and Clare, were a close family unit. Both excelled at school and moved to France after university. Xynthia worked as an overseas accounts manager for GoPro, in Biarritz, where she met Balthazar, and the couple lived in the French Pyrenees.

“Xynthia got all the family together in the West Country in the spring of 2014 to tell us she was pregnant. She wanted us all in one place and for it to be a surprise, which it was. Everyone was delighted,” Hawke recalls. “She wanted to have as natural a birth as possible, which isn’t that easy in France. But they found a natural birth facility attached to a hospital. They had visited it and met the medical team and discussed it all and everything was organised. But on the day itself, the labour was long and the birth just wasn’t happening.”

After a long labour, the clinic’s medical team, realising the baby was large and Xynthia was tired, decided to perform the C-section.

Iris says: “They took her to the operating theatre and Yannick said, ‘eee you later’. That’s when it happened. Yannick was there, my mum was at the house waiting for her daughter and baby grandchild to come home so she could help with the baby. Yannick and Isaac came home, but Xynthia didn’t. We realised something had happened, but we could never have imagined so terrible a thing happening. We were all like zombies.

“Our first reaction was disbelief – it was just unbelievable – and disgust. I am still disgusted with [Wauters]. You cannot be drunk and an anaesthetist. You have someone’s life in your hands and as an anaesthetist your job is to keep someone alive and that woman was in no fit state to be in control of anybody’s life.”

Questioned by investigators after Hawke’s death, Wauters was found to have an alcohol level of 2.16g a litre of blood and reportedly admitted a “pathological problem with alcohol”. The French drink-driving limit is 0.5g a litre. At her home, police reportedly found more than a dozen empty vodka bottles.

The clinic, which has since closed, and the hospital are facing charges and a second doctor, an obstetrician, is the subject of a separate investigation for “non-assistance of a person in danger” relating to events after the caesarean.

“I hold [Wauters] personally responsible for the death of Xynthia,” says Hawke. “She made a mistake because she was drunk. There is also chain of responsibility and she should never have been in that operating theatre. For my parents, this has ruined their lives. For me … she was my little sister. My only sister. And she’s gone. I don’t have another one and I never will. We are all living in limbo waiting for justice for Xynthia and Isaac. If Yannick didn’t have Isaac, I don’t know how he’d cope. At the same time he is bringing up a baby on his own, without the person he wanted to do it with. Isaac will be four this week. He knows he doesn’t have a mum like other children do, and while we do talk about Xynthia with him we don’t force it.”

The family’s French lawyer has told them the case should come to trial early next year. Until then, Hawke says their lives are on hold. After the tragedy, Wauters’ lawyer, Florence Hegoburu, told French reporters her client, who faces up to five years in jail if convicted, was not entirely to blame. “My client will assume her responsibilities in relation to the facts that she recognises, but she is not solely responsible. There are grey areas here, and the investigation will make them clearer.”

During a successful bail hearing two weeks after the tragedy, Wauters’ statements to police and an investigating judge were read out. “I drank a half bottle filled with a mixture of water and vodka. I wasn’t drunk. I was 70% capable,” she said.

Hawke says she and her family have been left deeply traumatised by what they have learned during the investigation and says they cannot move on until the trial happens. “Xynthia was a sister, daughter, girlfriend, she was great fun and a really amazing person. She should never have been in that situation in a hospital. Nobody should. All we can hope is that this woman goes to jail, that the clinic and hospital take responsibility and that it never, ever, has to happen to anyone again.”