A coroner has heard deeply distressing evidence that a 23-year-old British woman was shot dead by her father in the United States following an argument about Donald Trump and gun ownership.

Lucy Harrison, a fashion buyer from Warrington, was visiting her father, Kris Harrison, at his home in Prosper, a suburb of Dallas, when she died on 10 January. An inquest into her death is now underway at Cheshire Coroner’s Court.

On Tuesday, Lucy’s boyfriend, Sam Littler, told the court the couple had travelled to the US for a holiday and were due to fly back to the UK on the morning of the shooting.

Littler said Lucy often became distressed during conversations with her father about his ownership of firearms, a topic that caused repeated tension between them. The court also heard that Kris Harrison had previously attended rehabilitation for alcohol addiction.

On the morning of their planned departure, Littler said Lucy and her father became embroiled in a “big” argument about Donald Trump, who was due to be inaugurated as president later that month.

“Kris and Lucy ended up having quite a big argument which led to Lucy running upstairs and being upset,” Littler told the court.

He said Lucy challenged her father during the argument, asking how he would feel if she were sexually assaulted. According to Littler, Harrison replied that because he had two other daughters living with him, it would not upset him “that much.”

Roughly half an hour before the group was due to leave for the airport, Littler said Lucy was in the kitchen when her father took her by the hand and led her into his ground-floor bedroom. About 15 seconds later, Littler said he heard a loud bang.

“I remember running into the room and Lucy was lying on the floor near the entrance to the bathroom,” he said. “Kris was just screaming, just sort of nonsense.”

Lucy’s mother, Jane Coates, described her daughter as a passionate and deeply caring young woman. Lucy worked for fashion brand Boohoo and, her mother said, loved debate and discussion.

“She cared. She was passionate about things,” Coates told the court. “She loved to have debates about things that meant a lot to her.”

Kris Harrison did not attend the hearing to give evidence. His legal representative, Ana Samuel, made an application for coroner Jacqueline Devonish to recuse herself, arguing that the inquest was being conducted more like a criminal investigation than a neutral fact-finding process.

That application was strongly opposed by Lucy’s family. Lois Norris, representing Coates, described the move as an “ambush,” noting that Harrison was “the person in the room who shot Ms Harrison” and the only individual present when the fatal shot was fired.

The coroner rejected the application, allowing the inquest to proceed.

The hearing is expected to conclude on Tuesday, as Lucy Harrison’s family continues to seek answers about how a political argument inside a family home ended with the loss of a young woman described as “a real force of life.”