Nicki Crick, a professor of child psychology at the Institute of Child Development who was known for her love for sweets and “quirky enthusiasm,” died Sunday morning of cancer. She was 54.

Crick worked at the University of Minnesota for more than a decade, producing world-renowned research on relational aggression — the idea that people hurt others through manipulating relationships.

She served as the director of the Institute of Child Development from 2005-11.

Her work took her to Uganda, where she studied and helped children overcome their aggression.

Colleagues of Crick found lollipops in their mailboxes Monday morning following her death, and they “were certain they were from her.”

“She must have had someone put them in there,” said Maria Sera, one of Crick’s co-workers at the institute. “It was just heartbreaking but a little reminder of what a real sweetheart she was.”

Crick brought bowls of candy to every staff meeting, gave birthday cards to everyone in the department and dressed up in costumes for Halloween, said Megan Gunnar, director of the institute.

“She would put on full garb so you didn’t know who it was,” Gunnar said. “It was usually some black, ghoulish thing and she would run around and give candy to all the labs.”

Crick’s battle with cancer was “only a few weeks,” said Pete Ralston, an assistant at the institute who knew Crick for nine years. He said she was hospitalized near the end of September and then took a leave of absence from the University.

“Students have commented during Nicki’s illness how much she meant to them and how much she brought depth to their experience,” Ralston said. “They’ve said how much her enthusiasm and excitement really made for quality experiences.”

During the course of her career at the University, Crick made three trips to Uganda where she and her peers conducted research on the effects of wartime experience on children.

“Working with Nicki in Uganda was an incredible experience, and I was very lucky to learn under her supervision,” said Kathryn Hecht, a fourth-year graduate student in the Childhood Developmental Psychology program.

Hecht worked with Crick for several years, both at the University and in Uganda.

“She’s always been someone incredibly passionate about all of her work, but to see the enthusiasm that she had for this project in Uganda was inspiring,” Hecht said.

Crick’s research on relational aggression has brought stories like “Mean Girls,” where “nasty behaviors like gossip and threats destroy relationships and punish others,” to the forefront of psychology, Sera said.

There are school-based programs to reduce relational aggression because of Crick’s findings, Gunnar said, and her research is used to assess bullying.

“Some of her work that she has done at the University is world-renowned,” Ralston said. “It’s regarded very highly and reflects very well of the caliber of researchers we have here, and Nicki is truly one of the best.”

Gunnar agrees that Crick’s work greatly influenced the field and will be further developed in the future.

“She changed the whole field of developmental psychology with regard to relational aggression,” Gunnar said. “She’s a big deal. She was a big chief.”

Hecht said she plans to go back to Uganda this summer to collect the second wave of data for the project and continue Crick’s research.

“She has trained a cadre of wonderful students out there in the world now doing research,” Gunnar said.

There will be a memorial service for Crick at 10 a.m. on Dec. 1 at the McNamara Alumni Center. It will be open to the public.

In the meantime, there’s a table set up in the main office of the Institute of Child Development with flowers, Crick’s picture and a bowl of candy in her honor.

“People have been taking the candy all day,” Gunnar said. “Kind of like a comfort thing.”