Bethany Farrell, 23, of Colchester, Essex, was scuba diving off the idyllic Whitsunday Islands in Queensland, just a week into her gap year when she drowned in February 2015.
Farrell, an English graduate, was on an introductory dive trip with a friend when she panicked and drowned after becoming separated from her instructor, Chelmsford Coroner's Court heard.
Her father, Patrick, 48, called for the company - named in court as DL20 Trading Pty Ltd - to be prosecuted after she died on what was due to be a 12-month gap year.
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After the inquest, he said: "Ultimately, Bethany went on a paid-for organised trip and was completely let down.
"The whole point of an introductory dive is its an introductory dive.
"Legal proceedings are going ahead."
Caroline Beasley-Murray, the senior coroner for Essex, recorded a narrative verdict.
She told the court: "The deceased drowned whilst on an introductory dive in Blue Pearl Bay, Hayman Island.
"There were various failings in the way in which the diving activities were carried out."
Queensland's health and safety investigators found "failings" by the company included not allowing people to practise with their buoyancy devices or testing the competency of the first-time divers, the court heard.
Farrell, who graduated from an English literature and media course at the University of Southampton, arrived in Queensland on February 11 last year.
Six days later - on February 17 - she embarked on the dive with her friend, another novice and their instructor Fiona McTavish, the court heard.
Australian police officer Constable Syrrell Howard wrote in a statement read to the court that Miss Farrell separated from her dive group, possibly after they became "intwined" with a second team.
She was seen briefly surfacing before she "descended ultimately to her death", he said.
The Office of Industrial Relations, Queensland's equivalent of the Health and Safety Executive, said the diving firm risked the health and safety of Farrell and her two co-divers.
Its report said the trio should have had their basic swimming competency tested and been allowed to practise how to maintain a "positive buoyancy" before they went diving at around 4.30pm that day.
A post-mortem examination recorded Farrell's cause of death as drowning.
After the hearing, her mother, 51, paid tribute to her as a "real-life angel", adding: "She was lovely, she was just beautiful."
