The owner of the Phoenix has reported to police and denied a charge of recklessness, as divers have recovered the last body trapped under the capsized boat.
Phuket police chief Theerapol Thipcharoen said on Sunday that Woralak Ruekchaikal turned herself in to police on Saturday, one day after an arrest warrant was issued for her.
Ms Woralak was informed about the charge of recklessness causing death and injuries to others, and Pol Maj Gen Theerapol said the suspect denied the allegation.
She was in police custody at Chalong police station and police were to ask the Phuket Provincial Court for her further detention on Monday.
The court on Friday approved the arrest warrants for the boat owner and Onchan Kanhayothi, the chief engineer of the vessel. Mr Onchan acknowledged the same charge and was temporarily released.
The ill-fated boat carrying 89 tourists, most of them Chinese, and 12 crew sunk off the Phuket coast on July 5. Forty-seven visitors from China lost their lives in one of the worst sea tragedies in Thai history.
"Police are compiling evidence and will charge anyone whom the evidence points to," the Phuket police commander said.
The boat tragedy has led to the mass cancellation of hotel rooms in Phuket by Chinese tourists. Visitors from China comprise the leading nationality amongst foreign tourists.
Phuket governor Noraphat Plodthong said the identity of 46 victims had been verified, with 39 cremated in Phuket and seven others returned for ceremonies in their home country.
Divers on Sunday were able to recover the last body from underneath the sunken vesselafter battling strong currents and a solid sand bed.