However, while the reunion was supposed to bring the family together but, it has done the exact opposite.
Gill’s husband Carson, 66, and her sister started a sordid fling which grew into a full-blown affair.
Now the pair of cheats are living together near Perth, Australia, and are apparently getting set to tie the knot – even though poor Gill is yet to sign divorce papers.
Gill, from Calne, Wiltshire told The Sunday People: “I thought about Helen all those years and believed the reunion would be the cherry on the cake of my happy family life.
“Instead she had an affair with my husband. They’re shacked up in the sunshine and telling everyone what a happy life they have. It’s heartbreaking.
“I want to strangle her but it’s not all her doing, it’s him as well. They’ve both ruined my life.”
Gill, was just 16 and pregnant at the time she married Carson at Chippenham registration office in March 1971.
She had glamorous hair and wore a mini dress for the nuptials – with Helen, then 14, at her side.
Just days after the wedding, Gill’s parents emigrated to Australia alongside Helen and her sister, aged eight, and brothers 12 and 10.
The newlyweds moved into a flat in Derry Hill, Wiltshire, and nine months later bought a house in Calne.
They went on to have four daughters, now aged 45, 41 and a set of twins who are 40.
Gill always regretted losing touch with Helen but said her sister was never out of her thoughts.
In September 2014, Gill was elated after Helen got back in touch with her.
Helen had recently got married in a vineyard and within two weeks had flown over from Perth to see Gill.
Soon, the sisters quickly became inseparable.
However, Gill says there was a warning sign that she regrets not picking up on.
She said: “Helen said to me one day that I had a lovely family and she wished she’d had my life.
“She said she had had a s**t life so far and no one understood her.”
But what Helen failed to mention was that she had found a shoulder to cry on – Carson.
Helen returned to Oz but kept in touch with Gill and later returned to the UK in March 2015 for another three week visit.
However, this time she didn’t stay with Gill and instead rented a cottage 10 miles away at Royal Wootton Bassett.
Carson, a retired logistics manager, went over every day to help with lighting the fire as Helen said it was cold.
Gill said: “I should have suspected something was up because everything I suggested we do together, she turned down flat.”
In the end, it was Gill and Carson’s 40-year-old daughter who did become suspicious, checking Carson’s phone and computer.
Shockingly, she discovered that her dad and aunt had kept in touch ever since her first visit and things had turned sexual.
The night before Helen was due to return to Australia, the family had a showdown which saw her daughter confront her father outright.
Gill said: “I went numb and Carson completely denied it. He dragged me out of the house and we got a taxi home. He didn’t say a word.”
The next day, Carson reassured Gill that he loved her and denied anything had happened.
The love rat dismissed the messages as “a little silliness” on his part.
Gill chose to believe him and hoped that everything would go back to normal.
However, Gill’s life took another nasty twist a few weeks later when she collapsed with flu-like symptoms and was admitted to hospital.
She said: “Carson wasn’t with me most of the time. I’m certain he was talking to Helen.”
Even when their marriage finally collapsed in November, Carson wouldn’t confirm his affair.
She said: “The day he said he didn’t love me any more cut me in half so bad, I’ve never hurt so much.”
Meanwhile, Helen had already separated from her husband – leaving her free to be with Carson.
Gill has not spoken to Carson or her sister since their split but, after losing their father died last month, she flew to Australia – where she received a final kick in the teeth.
Relatives told Gill that Helen and were happy as could be and even sharing a home.
Gill said: “I couldn’t believe they had both got their fresh start and I have been left with nothing.”
Despite this, Gill added: “I still love Helen, she’s my sister.
“As for Carson, if he’d turned up on my doorstep two months ago I would probably have taken him back and said: ‘I forgive you’. But not now. They’re welcome to one another.”