They were hit by the trailer, carrying a county council mobile display unit, when it became detached from a van in Codsall, Staffs, on Friday.
Police and fire crews had to lift the trailer so paramedics could reach one of the 14-year-olds after the accident in Lane Green Road at 1540 BST.
She was airlifted to hospital in Wolverhampton. Police say neither girl has life-threatening injuries.
Sarah Damen, 37, was walking on the pavement in Bere Regis in Dorset on Friday when the crash happened.
Mrs Damen, a mother of three young children aged five, four and two, died at the scene.
Another woman, Suzanne Gee, and her daughter, Rebekah, three, are recovering from their injuries. The driver was arrested and bailed.
The 44-year-old man, from Wareham, had been arrested in suspicion of causing death by dangerous driving.
A red Land Rover had been travelling along the C6 Southbrook road to Wool in the village when its trailer detached, ploughing into the group.
Mrs Damen's children and her 44-year-old husband, Mark, have been comforted by relatives.