But as she climbed the “algae-covered” wooden planks on the mechanism, she fell off the side into a “much deeper” area of water at the park in Tamworth, Staffordshire.
After pupils and members of the public raised the alarm, theme park staff rushed to the ride and began a search.
Some 11 minutes after staff were alerted to Evha originally going into the water, Evha was spotted “face down”.
It was another six minutes before theme park staff were able to pull her out, when she was described as “lifeless”.
Despite CPR being administered at the scene and advanced life support by air ambulance medics, she was pronounced dead less that two hours later at Birmingham Children’s Hospital.
The ride, which opened in 1993, and features up to 21 boats each with a capacity of six people, remains closed following the incident.
Offering a “a wild ride” with “fast-flowing rapids”, riders must be at least 0.9m (3ft) tall, although those under 1.1m can ride if they are accompanied by an adult.
Opening an inquest into her death on Monday, assistant coroner for South Staffordshire Margaret Jones said Evha and her friends had been on the ride “without incident” accompanied by teachers, earlier that day.
The hearing was told that according to the theme park’s ride height restrictions, Evha was allowed aboard the vessel without an adult.
A signed risk assessment prepared by the school before the trip stated that a member of staff would be “allocated” to groups of five or six primary age pupils, like Evha, while the older secondary age pupils could supervise themselves.
DI Quilty said: “The member of staff allocated to Evha and her group remained at exit and did not join her group and her intention was to meet children as they came off exit.”
Meanwhile, three other member of staff boarded a different vessel, travelling four boats behind Evha’s.
A member of the theme park ride staff said he observed the “good behaviour” of Evha and her friends boarding their vessel.
But CCTV showed that as soon as the ride begun, Evha and some of the other girls were leaving their seats and not keeping hold of the safety rail.
DI Quilty, who led an investigation into the incident, said: “At no point do we actually see her sat (in her seat) on the ride.”
Describing the moment she was ejected from the vessel, he said: “Evha is sat out of the seats, in the gap (between the seats).
“She is sat down at this point in time, and when the boat makes contact (with the barrier) – at the worst possible time – she stands up and, as a result of the propulsion and force of the barrier, that propels her out of the vessel.
“She is just standing up and as soon as she makes contact with barrier she is pushed out, there’s nothing behind her and she naturally falls out.”
Dr Frances Hollingbury, a Home Office pathologist, said she had determined a cause of death of drowning, although it was initially recorded as a result of blunt force trauma to the chest.
She added that although Evha suffered multiple rib fractures, possible injuries to the lungs and a broken pelvis, she “wouldn’t have expected Evha to have died as a direct result of these injuries, without complications”.
The inquest continues.