The House select committee investigating the January 6 Capitol attack has subpoenaed Kimberly Guilfoyle, the fiancée of Donald Trump’s eldest son. House investigators issued the subpoena Thursday, after she had abruptly ended a voluntary interview with the panel last week.

The committee is investigating the events surrounding the insurrection at the Capitol last year, when a mob of Trump supporters violently attacked the building in a failed attempt to halt the certification of Joe Biden’s 2020 election victory.

The chairman of the select committee, Bennie Thompson, said in the subpoena letter to Guilfoyle that the panel was compelling her testimony because of her proximity to the former president and the rally that preceded the Capitol attack on January 6.

Thompson said the panel had been left with no choice but to force her cooperation.

“Because Ms Guilfoyle backed out of her original commitment to provide a voluntary interview, we are issuing today’s subpoena that will compel her to testify. We expect her to comply with the law and cooperate,” Thompson said.

Guilfoyle met virtually with the panel for an interview last week, but cut off questioning when she learned that select committee members Adam Schiff and Jamie Raskin – in addition to counsel – had joined the call.

After news of her appearance was leaked to news outlets, Guilfoyle refused to continue, and her lawyer accused the select committee of trying to “sandbag” her and not keeping participants limited to committee counsel, according to a source familiar with the interview.

Members of the select committee are actively involved in the investigation, and are almost always present at depositions. But Guilfoyle’s lawyer said in a statement that the panel sought to use her cooperation as a “political weapon” against Trump.

“Ms Guilfoyle, under threat of subpoena, agreed to meet exclusively with counsel for the select committee in a good-faith effort to provide true and relevant evidence,” Joseph Tacopina, Guilfoyle’s lawyer, said in a statement after she halted her interview.

“However, upon Ms Guilfoyle’s attendance, the committee revealed its untrustworthiness, as members notorious for leaking information appeared,” Tacopina said, referring to the two congressmen Schiff and Raskin.

The lawyer for Guilfoyle added that after he asked for a break to address the issue with House investigators, the select committee leaked the breakdown in proceedings to reporters. A spokesman for the select committee has denied Tacopina’s claim.

The select committee did not address those complaints on Thursday. But the subpoena authorisation suggested the panel does not believe the matter precludes her from testifying about her contacts with Trump and rally organisers on January 6.

The panel additionally noted that it had earlier informed her legal team that members would be present in her interview and even offered to reschedule Guilfoyle’s interview, but she declined.

Guilfoyle was notably present for an Oval Office meeting that morning when Trump pressed then Vice-President Mike Pence to reject slates of electors for Biden at the joint session of Congress and thus return him to power, the subpoena said.

House investigators added in the subpoena that they were also interested in Guilfoyle’s claims that she helped fund the “Save America” rally that preceded the Capitol attack, as well as discussions with Trump about who spoke at the rally.

Guilfoyle told at least one rally organizer that she had “raised so much money for this. Literally one of my donors Julie at 3 million” – a reference to Julie Fancelli, who did in fact finance the event, the panel said.