A disciplinary hearing by the General Teaching Council for Scotland found she had been unable to carry out her duties during a visit to Castle Toward outdoor education centre in Dunoon in March 2008.
Mrs Bruce, 56, was in charge of a group of P6-7 children and staff from St Mary's Primary in Paisley. After the trip, she was suspended and an investigation was launched by Renfrewshire Council. But she was granted early retirement and the procedure was never completed.
The committee heard that staff shared a drink after Mrs Bruce told probationer teacher David Keene to buy a bottle of vodka. They had a couple of drinks but it was not until the following day that anything "untoward" happened, according to Karen Park, a teacher at St Mary's, who was also on the trip.
While leading an activity in the late afternoon, Mrs Bruce issued "ridiculous instructions" that "did not make any sense" and were "confusing for the children", Ms Park told the committee, forcing her and Mr Keene to take over.
That evening, when the children were meant to be asleep, Mr Keene and Ms Park, who were supervising the boys' corridor, said they heard Mrs Bruce, under the influence of alcohol, leading the girls in song.
The depute head of the education centre at the time, Vicky MacNeill (now Neville), told the committee she was in "no doubt" Mrs Bruce was under the influence of alcohol during the trip. She had reports from her staff "questioning how sober Mrs Bruce was" and domestic staff had cleaned up her bathroom after she had been sick, she said.
When Mrs Bruce spoke to the children before they left the centre there was a look of "mistrust" on their faces, Mrs Neville said. This upset her because the children should have been able to "trust implicitly" the leader who came away with them, she continued.
Mrs Bruce denied the charges but did not attend the disciplinary sub- committee hearing. Her solicitor, Andrew Gibb, pointed out that she had an unblemished record and that, while the head of the school had "concerns", no formal action had been taken regarding an "inherent drink problem".