There had been an “incident” at the Houses of Parliament where her 10-year-old son, James, was away on a school trip from Luddendenfoot Academy.
She ran to her TV and watched the chaos unfold, not knowing whether James was inside or outside the building.
She said: “It was unbelievable. It’s just not something you imagine happening. When it’s your child it’s so incredibly distressing.
“The children were so giddy and happy when they left, smiling and waving us off.
“It was not knowing about what he had seen or witnessed and I wasn’t there to look after him.”
She was fixed to the news all day with her phone in her hand as details of the attack emerged. Through continual updates from school staff she was told James was locked inside the building with his teachers and schoolmates, and was safe.
And it was the “incredible” efforts of school staff that kept her going through the day when she was sick with worry.
“James was with the headteacher Mrs Denham and Mrs Webb, the deputy. They are absolutely lovely and they have great relationship with the children.
“They kept letting us know they were safe. The school is like a family. I can’t thank them enough for looking after my son,” she said.
The children were released from parliament later that evening and taken back to their hostel to call home.
Calderdale Council said, after making sure that all pupils from the district were safe, parents could collect their children from London or let them continue with a scheduled Harry Potter tour.
James decided to stay. “He didn’t want it to ruin his trip,” said Mrs Shackley, of Ovenden.
She praised the “amazing” response from the emergency services and paid tribute to the victims of the attack.
More than 50 Calderdale schoolchildren were in London on the day with pupils from Siddal Primary School, Halifax; Field Lane Junior and Infant School, Brighouse, and Cliffe Hill Community Primary School, Lightcliffe, Halifax, also visiting the city.
The council’s director for adults and children’s services, Stuart Smith, said: “I’d like to praise the work of staff at the schools involved for keeping the children safe and parents informed and reassured throughout.”