Rebecca Turner and her boyfriend Sam Melnick were found dead on the floor of her room by hotel staff on 15 March last year.
They had unwittingly taken a fatal mixture of drugs, an inquest heard.
Ms Turner’s parents said their 36-year-old daughter, from Bexhill-on-Sea in East Sussex, thought she was taking cocaine on the night before she died.
However, the mixture she took actually contained morphine, codeine and several other substances, the inquest was told.
Anita Turner has travelled to Thailand three times since her daughter’s death, and plans to go out again next month.
Speaking outside East Sussex Coroner’s Court, she warned other travellers against taking drugs abroad and criticised Thailand’s police force.
She said: “They [Thai police] promised me details in six months’ time and that was about eight months ago. I’m still waiting.
“All the police try to do is just cover it up and they got mad at me one day because I told them that and they told me I was lying.
“There is a text message [from Rebecca] talking about a little bit of cocaine. She thought it was cocaine.”
During her trips, Anita Turner has continued the charity work her daughter had begun.
She described her daughter as “fun, bubbly, always partying, always laughing, always smiling”.
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Assistant coroner Laura Bradford recorded a conclusion of a drug-related death and said the medical cause of death was drug toxicity.
The coroner said there was “no evidence to suggest she was intending to die”, adding: “I have evidence from Rebecca’s family that her mental health was stable and her mood was in fact good.”
Sky News has approached the Royal Thai national police and the Thai embassy for comment.
