Chinese tourists accompanying Wang Qi, 32, have raised questions about the woman's death.
The operator of the Flying Squirrel at Pong Khrai village in Mae Rim district told them Wang had died of heart failure on the zipline adventure ride on Sunday afternoon. A post mortem examination at Nakornping Hospital concluded she had suffered a broken neck and shoulder bones.
The tourists to asked the Chinese consulate in Chiang Mai to help find out the real cause of her death.
Pol Col Suchart Kan-ngern, chief investigator at Mae Rim police station, said police were rushed to the scene upon being alerted that the Chinese woman had died of heart failure on the treetops ride.
Pol Col Suchart said he would today follow up the case and promised to ensure justice for all, Thai media reported on Tuesday.
A source said witnesses told police investigators that Wang was about to reach a spot on the ride where two male staff stood ready to take hold of her, but they allegedly made a mistake and the woman fell to the ground.
The aerial adventure has 32 treetop stations. Customers swing, abseil, bicycle, skateboard, held by slings attached to their bodies, from one tree platform to the next, the longest ride being 600 metres between stations. This thrill ride is popular with tourists.