McCollum was caught trying to smuggle 24lb (11kg) of cocaine worth £1.5 million out of Peru with accomplice Melissa Reid in 2013.
The pair, nicknamed the Peru Two, were jailed for six years and eight months after admitting the crime, but were freed in 2016 after striking a deal with Peruvian authorities.
McCollum, from Dungannon, Co Tyrone, returned to Northern Ireland in August.
Writing on Facebook, she told her followers: “Now that I have the chance I just want to thank everyone who has supported myself and family through these past few years.
“Please know I truly appreciate each one who cared and had my back.
“Thank you for all the sweet messages I have not got reading them all just yet or got a chance to reply to them but I will definitely make a good attempt to get back to you all.
“It has been a long ride to get where I am today but it just shows that when we fight hard enough for something we can achieve.”
McCollum and Reid, from Lenzie, East Dunbartonshire, travelled to Peru on August 15 2013, and were caught trying to leave the country with the Class A drug at Lima Airport two days later.
They faced the prospect of a maximum 15-year prison term but struck a behind-closed-doors plea bargain to secure the shorter sentence.
Alongside a selfie showing a blonde hairstyle, McCollum told friends of her hopes for the future despite her criminal reputation.
She said: “When one door closes, another opens; but we often look so long and so regretfully upon the closed door that we do not see the one which has opened for us.”
After their arrest the pair said they had been forced to carry the drugs under duress.
However, Reid told the Scottish Sun on her return how she travelled to South America to have a story to boast about to friends on the Ibiza party scene.
She was offered 5,000 euro (£4,100) to fly to Argentina, spend a few days sightseeing and return to Europe with a package in her luggage.
“My life will never be the same,” she told the newspaper.