Amid what seemed at first glance a summer barbecue with large spreads of food and drink, music and dancing, and friends embracing and chatting, there was a somber reminder of why hundreds gathered at Liberty Lands Park in Northern Liberties yesterday afternoon.

Two large white sheets hung between two trees and those that gathered to remember Sabina Rose O'Donnell scrawled their final goodbyes to their slain friend with brightly colored Sharpie markers.

"Thank you for showing me what a true friend is," one message read. "You are bigger than this life," said another. "Take Back the Night for Sabina," read a third.

O'Donnell, 20, was found dead June 2 in a vacant lot just north of Girard Avenue between 4th and Orianna streets. Police said she had been beaten, strangled and sexually assaulted. Her killer remains on the loose.

"She was exactly what everyone has said, a sweet girl who always had a smile on her face," said a woman named Eimav, who asked that her last name not be used.

The memorial service was organized by Tommy Up, O'Donnell's boss at PYT, a bar and restaurant at the Piazza at Schmidts.

"She would have loved this and loved being here today," Up said.

As friends and family ate, drank and danced, they shared fond memories of O'Donnell.

"She was happy, energetic, and sweet," said Talia Bella, 28.

Bella sang "Somewhere Out There" from the movie "An American Tail" to begin the memorial service at the park on 3rd Street near Brown.

She had been practicing the song to record for a children's CD but when she was approached about singing something yesterday she thought it was fitting for Sabina because of her good nature.

"She was just this innocent bubble of joy, uncorrupted by the city and the world," Bella said. "She's dancing somewhere out there."

As mourners arrived throughout the afternoon, they placed flowers and potted plants on a path leading to the stage.

A dance company from the Gwendolyn Bye School in West Philadelphia, where O'Donnell took dance lessons from age 6 to about 14, performed for the crowd and offered condolences to O'Donnell's mother, Rachel, and stepfather, Mark Rounds.

"She was a very bright, intelligent child, very talented in many ways," said Gwendolyn Bye, the owner of the studio. "I saw a charisma, an energy. She was radiant, people came toward her."

Later in the day, O'Donnell's mother and stepfather addressed the crowd.

"I have never known a love as pure and devoted as the love I received from Sabina," Rounds said.

"People keep telling us that Sabina's in a better place," Rachel O'Donnell said. "But any place that has Sabina in it is a better place."