Yesterday, being a Thursday, when prisoners convicted on heroin- related offences are allowed visitors, several dozen Thais and a handful of westerners were waiting quietly in the piercing heat of the forecourt for the afternoon visiting session to get under way.
Inside, sitting behind the iron grille, on the prisoner's side of the noisy visiting corridor, Patricia, now 20, looks very different from the distraught teenager in the photographs of three years ago when she and Karyn were detained for drug trafficking.
With neat curly hair, a bit of lipstick, and a conspicuous silver crucifix around her neck, she manages to look stylish even in her regulation blue prison dress.
She greets visiting strangers warmly as a welcome break from the monotony of life at Lardyow. 'It's pot luck when we are allowed to see people.'
But when she realises the person is just another reporter, her suspicion and disappointment are intense.
'People just don't realise how much damage they have caused my family,' she said.
Patricia has often been seen as the villain of the affair, leading her friend astray. The two girls were sentenced respectively to 18 years 9 months, and 25 years.
Patricia is curious but not particularly optimistic when told about the latest developments in the case, for false hopes have been raised too many times.
The Independent revealed yesterday that the Government Chemist had cast serious doubt on the main plank of the evidence used by the Thai authorities to convict the two women.
Dr Terry Gough, head of the Government Chemist's Forensic and Customs Division, said in a letter to the Foreign Office that it was impossible for the 30.5kg of heroin that the two girls were found guilty of carrying to have fitted into the bottles and tins the Thai police said were found in their suitcases.
Three years later, Patricia gives the appearance of coping with life in prison. She now speaks fluent Thai, is teaching an older Thai inmate English, and has become a voracious reader.
'I really appreciate literature. It is difficult to get good books in here. When the missionaries bring them in we share them around.'
At the moment she is reading Mansfield Park, by Jane Austen.
Arriving at Lardyow the visitor sees a wooden-slatted, cream Thai- style house with a lily pond near by.
Patricia described the reality of life inside. 'It's a system here. They make you do things when they want you to do them.'
Lardyow has about 1,500 women inmates. Patricia has to sleep in a crowded dormitory of 125, lying on a mattress on the floor, wedged up against her neighbours.
Each day, everyone must get up at 6am and be ready after breakfast to start work in one of the prison factories. At the moment she is sewing smocking for which, like all the prisoners, she receives no pay.
There appear to be no opportunities for studying or vocational training. Nor is there any exercise programme, although Patricia said someone once tried to organise aerobics.
Told she was looking well, she said: 'They (the other prisoners) all say, you've got to look after yourself physically, or you go mentally.'
Time passes slowly. 'One year in here is like five years.' For foreigners, the weekly treat comes on Sunday evening when they are allowed to spend two hours watching videos.
She did not do anything on her 20th birthday. 'I tried not to think about it,' she said.
'When I came here I was very young,' she volunteered at one point. We do not talk about her arrest and conviction. But asked how the past three years at Lardyow changed her, she simply said: 'Behind bars, I have become a woman.'
Karyn Smith is two years older than Patricia. Yesterday she was suffering from a stomach upset. 'The water here is not so good,' explained Patricia. 'She is not going anywhere today.'
Karyn, on her lawyer's advice, rarely sees unexpected visitors. Patricia said that nowadays the two girls have an 'understanding' but are no longer particularly close.
Last year there was speculation that the two girls might receive a Thai royal pardon on the occasion of Queen Sirikit's 60th birthday in August. But it was not to be.
Did Patricia still look to the future with hope? 'It's all you've got inside here.'
She was brought up as a Catholic. 'There is a lot of controversy here (in Lardyow) about religion . . . but it's in your heart, isn't it?'
Did she think about being released? 'When my time comes, it comes,' she said.
Next year she should be eligible to transfer to a British jail to complete her sentence under an agreement between London and Bangkok.
On Monday, her parents, Frances and Patrick Cahill, will be paying a rare visit.
In May 1991, both travelled to Thailand for her trial. Her father was able to visit her last year, but this will be the first time for two years that Patricia has seen her mother.
'It's going to be very emotional,' she said yesterday.
She will try to negotiate with the prison authorities for extra visiting time for them.
Yesterday, after half an hour, the warden who had been patrolling the 3ft gulf between the visitors' and prisoners' grilles motioned that the session was over.
For a few more minutes, Patricia continued talking, and then followed the others out of the room, and back to the routine of an afternoon's smock making.