Hillary Clinton has dropped out of Fortune’s Most Powerful Women Summit, where she was scheduled to speak along with Hawaii Rep. Tulsi Gabbard and former Department of Homeland Security Secretary Kirstjen Nielsen.

The event, slated for later this month in Washington, D.C., touts itself as “the world’s most extraordinary leadership community” assembled for “wide-ranging conversations that inspire and deliver practical advice." The former secretary of state on Friday removed herself from the list of speakers, citing a scheduling conflict. However, a person close to Clinton claimed Nielsen's appearance on the docket may be the real reason behind her pullout.

"We work with a lot of activists who are trying to do their best to improve this horrible situation down at the border,” the person told Slate, citing Clinton’s support for organizations that advocate for asylum applicants and immigrants. “At the end of the day, it’s an easy decision. You have to side with them."

The person added, "While there’s an argument to be made to hear all voices, there are those who fall outside of what should be the band of acceptable behavior and public policymaking" before describing actions taken by Nielsen’s DHS as “one of the most horrific things that we’ve had to bear witness to within our borders in modern political history.”

More than 51,000 people have signed a petition urging Fortune to drop Nielsen from the event but to no avail.

"Fortune strongly believes that interviewing Nielsen — and other key figures from the private and public sector, however controversial — is important journalism and provides us an opportunity to ask substantive questions in front of our viewers and readers," the company said in response.

Also still set to speak at the event are several business executives, journalists, scholars, and elected officials. The list also includes Anita Hill and Gabbard, with whom Clinton has recently traded barbs.

On Thursday, the 2016 Democratic presidential nominee accused Gabbard of being a "Russian asset" that the foreign nation is "grooming" to spoil the 2020 election for the Democrats by launching a third-party run. Gabbard hit back on Friday, calling Clinton "the queen of warmongers, embodiment of corruption, and personification of the rot that has sickened the Democratic Party for so long." The Hawaii congresswoman, who remains a major in the Hawaii Army National Guard, also called Clinton's attack an attack on all veterans.