Writing from her cramped prison cell in Peru, the Scot said her pursuit of wild thrills in Ibiza was the reason behind her eventual imprisonment.
Reid, who turns 21 today, travelled to the Spanish island last summer for a working holiday before being drawn into a major drug-smuggling operation.
She was then arrested at Lima Airport last August after she and accomplice Michaella McCollum, 21, were caught with cocaine hidden in their suitcases.
One year on and Reid, of Lenzie, insists she has a "different head on her shoulders" after her time in jail.
She said: "A year ago today, if someone was warning me of the dangers of drug smuggling, I would probably tell them how I would not be so stupid and how it would not happen to me. But look at me now.
"It's not smart, it's not big and definitely not clever. As glamorous as the drug lords make it out, it's not."
She added: "Who knows, I might even be back in Ibiza one day myself, although with a different head on my shoulders.
"I will also now be watching my back for years to come and double-checking the door is locked every night because, as everyone knows, drugs is a big boys' game."
Reid's parents, Debbie and Billy, are currently visiting her at the Ancón 2 prison, situated just over 20 miles north of the capital Lima.
Accompanied by a 21st birthday cake, the duo were able to celebrate the milestone in person.
Mrs Reid said: "This time last year I thought maybe Melissa might be home for her 21st. Obviously not.
"She's not happy but she's resigned to the fact she's there and she's just got to get on with it day by day.
"She needs to be punished for what she did."
Pending official clearance from Peruvian officials, both Reid and McCollum will soon be transferred to a UK prison.