After turning 18, she landed a job as a counter clerk at a post office in London, bought a house with her boyfriend, and for a year or so, her life seemed idyllic.
Then, one day in February 2001, her life would change forever.
It is almost 18 years since Miss Felstead, now 36, was questioned about a shortfall in her till at the Camberwell Green Post Office where she worked, and it is clear it has left mental scars that will never heal.
Sitting on the sofa at her house in Brookside, Telford, her voice quivers as she recalls the events that followed. She tells how she has twice tried to take her own life, and the best part of two decades on, she is still haunted by nightmares and takes regular medication for Post Traumatic Stress Disorder.
Miss Felstead is one of 557 post office staff who are fighting to clear their names after being blamed for financial discrepancies at the branches where they worked. They say the shortfalls were caused by a faulty computer system which the Post Office had impose on them.
Just 19 years old at the time, Miss Felstead vehemently denied the allegations, and says it was her protestations of innocence that led to her being jailed for six months in June that year.
"My family paid the £11,500 hoping it would mean I did not have to go to jail, but the judge said I had shown no remorse, and had been stealing from Old Age Pensioners," she says.
"I served three months in Holloway, and I saw a girl hang herself, that is something I will never get out of my mind.
"When I came out, I was on a tag for three months, which meant I couldn't work.
"I lost my job, which meant I couldn't keep up with the mortgage payments, and I lost my house. I now find it impossible to trust people."
Her ordeal began when she returned to work from holiday in 2001, and was asked to produce a till print off.
"My till was short of £11,503.28," she says. "Because it was my signature on the paperwork, I was liable for the loss. I was accused of stealing it."
After being questioned by her manager, the matter appeared to blow over. The youngster returned to normal duties, and hoped that would be the end of the matter.
But a fortnight later, four men – two police officers and two Post Office investigators – made an early morning call at the home of her boyfriend's parents.
"They knocked on the door of my in-laws at stupid o'clock in the morning," she says.
"I wasn't there, I didn't live there, but because I was not at my home – I was staying with friends – that was the next place they went to. They came to take me down to the police station."
When she heard what had happened, Miss Felstead handed herself in at the police station, where she was subjected to what she describes as a very forceful interview.
"They kept saying 'you have stolen the money', and I kept saying that I hadn't," she says.
"After that I had to go back for another interview, again I had no legal representation, I was perhaps a bit naive.
"They just kept asking me 'Did you do this? Did you do that? What happened with that?'
"I answered the questions as much as I could, and they suspended me."
She says the Post Office were given full access to all her bank accounts, which showed there had been no significant payments into her account. She says she also invited the investigators to search her house, but they never took up the offer.
"During the interview they made comments that me and my family were going on holiday, and did I steal the money to pay for the holiday, I just said 'I haven't taken any money'," she says.
"They just kept going on, 'did you take the money for this?' and I just said 'I didn't take any money'. I was 19, and I felt intimidated.
"I tried to kill myself twice while awaiting trial by taking an overdose."
In prison, she was placed on suicide watch, and witnessed regular fights and drug-taking.
But it was the sight of discovering an inmate who had hanged herself which had left the biggest mark on her.
"I had a job in there taking hot drinks to the cells, but in this one cell there was a girl, she was hanging, she was dead."
Before her conviction, Miss Felstead had hopes of a career in financial services, but that was in tatters after her release from prison. She found work – many employers were surprisingly understanding when she explained her past to them – but many career paths were now understandably shut off to her.
It was about five years ago, when news began to emerge about other post office staff with similar stories to hers, that she realised she was not alone. The Shropshire Star reported the case of former Shrewsbury sub-postmistress Rubbina Shaheen, who is also battling to have her conviction overturned after being jailed for 12 months for false accounting. Mrs Shaheen said a fault with the Post Office's Horizon computer system led to a £43,000 shortfall appearing on her balance sheet, which led to her being jailed in December 2010.
Miss Felstead attended a meeting of Justice For Subpostmasters Alliance, led by former sub-postmaster Alan Bates from Conwy in North Wales, and discovered there were hundreds of post office staff across the UK who claim to have been wrongly blamed for financial discrepancies. They claim the shortfalls have been caused by a fault with the Post Office's Horizon database, which logs all transactions carried out by individual branches.
The Post Office responded by hiring a team of forensic accountants from Second Sight. The Post Office said the team found no evidence of systemic problems with the system, but Second Sight accused the Post Office of misrepresenting its findings. Managing director Ron Warrington said his report had found Horizon was 'not always fit for purpose', and that faults with the system could have led to the discrepancies which led to some of its users going to jail.
A group action by 557 former post office workers, including Miss Felstead, is now being heard in the High Court in London. The Post Office is fighting the claims, and insists it has full confidence in the Horizon programme. Miss Felstead and the hundreds of other post office staff are waiting to hear if it clears their name.
The action has meant that Miss Felstead has had to explain her past to her three children, aged 14, 12 and eight. But she says whatever the outcome of the hearing, nothing will ever make up for the ordeal of the past 18 years.
"I have lost friends, family friends didn't want to speak to me, they believed I had taken money," she says.
"They could give me a million pounds, but no amount of money will make up for the impact this has had on my life."