Gilmer, 26, knew Gabriel Zimmerman, Rep. Gabrielle Giffords' staff member who died in the rampage, and became nauseated when she learned of his death.
"I was in shock and just kept crying and crying," Gilmer said.
Gilmer sent a Facebook message to 90 of her friends Sunday. The message spread to thousands of others, and hundreds volunteered to help and donate money to the "divine guard."
"It's going to be a silent, counter protest. It's not about us. It's about protecting the family," Gilmer said.
Of the more than 3,000 people who have committed to donning white, 30 of them will wear angel wings with the idea of blocking the Westboro protesters' signs.
"We're hoping to have people dressed in white, lining the streets to show a brightness and hope, to show ...Tucson that we love you ... and we support them," Gilmer said.
The 30 "angels" have undergone training.
"When you train people to be angels, they are helped with understanding what they're going to be facing. They're given meditation techniques. They're taught ways to avoid violence ... ways to avoid confrontation," said Katerina Sinclair of the University of Arizona's Frances McClelland Institute for Children, Youth and Families, who will lead the training.
Sinclair said the use of the angel wings is a tool that's been used to counter the Westboro Baptist Church since it protested Matthew Shepherd's funeral in 1998.
"Their job is to stand there, block the signs, and they're the angels that stand between hate and everyone else. They don't engage, they don't respond. It's kind of like having a very divine guard," said Sinclair.
Gilmer herself, though, will not be among them.
"I'll organize it, but I don't think I can handle it. It's a little too close to home," she said. "If Westboro said something ... I would probably want to respond."
Gilmer said that her group stands ready to counter any Westboro picketers at any sites related to the shooting.
"If there's a threat of them, we'll be there," Gilmer said. "They're going to bring hate, intolerance, ignorance ... we're going to bring love."
ABC News' Russell Goldman contributed to this report.