The Belfast nightclub hostess who was reported missing by her family on the Spanish island of Ibiza, but later turned up in jail in Peru, could face up to 25 years in prison if found guilty of trafficking drugs.
The National Police of Peru said they found more than 24lb of cocaine - thought to be worth around £1.5m (€1.7m ) - hidden in food in the luggage of the two women.
Ms McCollum Connolly, who holds an Irish passport, was at the centre of a Facebook and online social media appeal, backed by Irish sports stars, desperately seeking information about her whereabouts over the past two weeks.
However the Republic of Ireland's recently retired Consul General in Lima, Michael Russell, said the two women could face up to a quarter of a century behind bars if convicted.
The severity of any sentence would relate to the size of the drugs haul. If they were convicted of possession of the lesser amount allegedly found in their own luggage, a penalty of seven years could be expected, he said.
But if one was found guilty of being responsible for the overall haul of more than 24lb in both sets of luggage, they could be imprisoned for between 15 and 25 years.
Inmates can apply for parole after serving a third of a sentence in some circumstances.
Mr Russell described the conditions in Peruvian jails as horrible.
"They are pretty dour and pretty horrible," he said.
"It's all a matter of money, quite frankly. You have to buy your space, you have to buy your food. If you don't have money you suffer quite a lot."
Mr Russell retired at the end of last month, and Ireland has not replaced its Honorary Consul General in the Peruvian capital.
"It's being handled by the British embassy," he said.
The ex-diplomat said there is an Irish Peruvian chamber of commerce and an ad hoc Irish committee that has in the past helped Irish citizens imprisoned or hospitalised in the country.
In Peru, the State will appoint a solicitor if the defendant does not have one but Mr Russell said they are "not always the best" lawyers.
Mr Russell said Peru does not like keeping foreign prisoners for a number of reasons, including cost, which can be to the benefit of anyone from overseas convicted in the country.
The pair were stopped at the international airport's Air Europa counter and the drugs allegedly found in their luggage.
Diplomats have confirmed they are helping an Irish woman and a British woman arrested in Peru over alleged drug trafficking offences.
The Foreign Office in London confirmed it was helping a British national.
"We are aware of the arrest of a British national in Peru this week and are providing consular assistance," a spokeswoman said.
The Department of Foreign Affairs said it was also providing consular assistance to the family of an Irish woman being held in Peru on suspicion of drug trafficking offences.
From Belfast, Ms McCollum Connolly holds an Irish passport. The photography student had gone to San Antonio in Ibiza in June on a working holiday where she was looking for work as a dancer and nightclub hostess.
Her family said she usually phoned home every two to three days and they became concerned when she had fallen out of contact for more than 12 days.
Ms McCollum Connolly and Ms Reid were detained at the Jorge Chavez International airport as they tried to board a flight to Madrid, which was travelling on to Palma Mallorca, police in Peru said.
Ms Reid's family is reported to be in shock after learning about her arrest.
Her father William, 66, spoke to the Sunday Mail from their family home near Lenzie, East Dunbartonshire. He said: "We don't know anything, we haven't been told anything.
"We don't have any new information. We are not in a position to elaborate.
"We're in the position where we are just trying to come to terms with it."
He told the paper it was "too early" to say whether any of the family would travel to Peru.
According to her profile on social networking site Facebook, Ms Reid is a former pupil of Lenzie Academy.
She worked as a sales adviser at Scottish and Southern Energy in Glasgowbetween June 2010 and July 2011 and had also worked for clothes store Next.
Ms Reid flew to Ibiza in June and lists the island as her current location.
She had posted numerous pictures of herself with friends on the island. Her last post was on July 21.