The lawyer representing Michaella McCollum has said he is unable to disclose the details of the hearing that took place on Tuesday.
Peter Madden said McCollum accepted the charges and a sentencing hearing will take place next Tuesday 1 October.
Madden said: "I intend to travel to Lima next week to attend the sentencing hearing and after the sentence is handed down by the judge, it will be possible make further comment."
More top news
One person has been arrested and no security personnel were injured, the Secret Service said.
It is the fifth publicly known guilty plea in the probe into possible collusion between the Trump campaign and Russia during the election.
Louella Eve Fletcher-Michie, daughter of Holby City actor John Mitchie, died last year at the Bestival music festival in Dorset.