McCollum and Melissa Reid, from Scotland, were imprisoned in 2013 for six years and eight months after admitting trying to smuggle cocaine worth £1.5 million from Peru to Spain.
In her first interview since being released, the Co Tyrone woman said: "I've forgotten the things that everybody takes for granted in life.
"Seeing the sun, seeing the darkness, seeing the moon and the stars, things I haven't seen in almost three years."
McCollum was freed under new legislation on early prison release introduced in Peru last year.
She had served two years and three months.
It is anticipated she will have to remain in Peru for a considerable period as part of her parole conditions.
Reid remains in prison in Peru.
She has been seeking to serve the remainder of her sentence closer to home in Scotland.
McCollum has been interviewed in Peru for a documentary that will be aired on RTE One on Sunday night.
In it, she acknowledged the potentially devastating consequences if she had successfully smuggled the drugs back to Europe.
"I probably would have had a lot of blood on my hands," she said.
"I potentially could have filled Europe full of a lot of drugs.
"I could have potentially killed a lot of people, not directly but I could have caused a lot of harm to people."
She added: "I made a decision in a moment of madness. I'm not a bad person. I want to demonstrate that I'm a good person."
McCollum, from Dungannon, and Reid, from Glasgow, were caught with the haul at Lima airport on August 6 2013 attempting to fly to Spain.
They had claimed they were forced into carrying the drugs but pleaded guilty to charges later that year.
The pair were caught trying to board a flight with 24lb (11kg) of cocaine in food packets hidden inside their luggage.
McCollum and Reid faced the prospect of a maximum 15-year prison term but struck a behind-closed-doors plea bargain to secure a shorter sentence.
The pair had previously been held at Lima's Virgen de Fatima prison but were moved to the Ancon 2 prison, where McCollum was reportedly crammed into a cell with 30 other prisoners with poor sanitation and toilet facilities.