The accident occurred when a car skidded in front of their coach, causing it to swerve off the road and overturn.
The dead woman and an 11-year-old boy who suffered leg injuries had to be cut from the wreckage by emergency services.
Spanish police named the dead woman as Dawn Mary Parker, aged 30. The car driver, a 22-year-old Spanish man, also died.
Holiday company Sunworld said 13 holidaymakers were still in four hospitals in the island's capital, Palma.
The accident happened just before 1am local time, near Lluc Mayor, close to Campos, about 12 miles north of Palma.
The tourists had been to an "extravaganza" at Son Amar, a club where they were treated to dinner and a show.
They were returning to their hotels on the east coast of the island, in and around Calas de Mallorca when a Volkswagen Golf skidded into the path of the coach, hitting the front of the vehicle, Spanish police said.
The coach was carrying 57 Britons, one of them a representative from Sunworld.
A number of the holidaymakers, whose ages ranged from five to 93, suffered minor injuries, while 11 passengers escaped unhurt.
Director of operations for Sunworld, Manny Fontenla-Novoa, said: "The passengers are still pretty shaken up. Obviously, they have gone through a fairly horrific experience.
"We are trying our best to help them. Those that want to come home can. The first may be able to fly back today although obviously we don't want anyone travelling in shock and are seeking medical advice on that."
Friends and relatives were given an emergency number to ring - 0113 236 1777.Reuse content