Now Red Paw is her full-time endeavor. Her home in South Philadelphia is the organization's headquarters. She shares her residence with her partner, Lori Albright, who also is chief operating officer for Red Paw, and, as of last week, a variety of dogs, cats, turtles, and lizards that are either pets or animals displaced by fires.
"There is no organization in the country doing what we're doing," said Leary, 36.
The need is certainly there. In Philadelphia and its four suburban counties last year, Leary's group assisted more than 450 animals affected not only by fires, but other catastrophes such as building collapses.
"Jen Leary is a jewel," said retired Philadelphia Common Pleas Court Judge Renée Cardwell Hughes, chief executive officer of the American Red Cross of Southeastern Pennsylvania.
"Her tireless energy and commitment to the community and our pets make her and Red Paw critical members of the disaster response in our region," she said. "We would not be as effective without Red Paw as families will not leave their pets."
On Jan. 10, 2011, Leary's engine company responded to a five-alarm fire at the Windermere Court Apartments in West Philadelphia. When she got home that night, she was flooded with calls and messages about animals still inside the building. As it turned out, residents were not allowed back for weeks. One cat was trapped for 49 days but somehow survived, Leary said.
"This was the birth of Red Paw, this fire," she said.
Early on, Leary's credentials as a firefighter and a Red Cross volunteer gave Red Paw credibility. Nearly three years later, the nonprofit has a track record that she hopes to leverage into large grants and donations to fund and expand her operation.
The hard work is paying off.
Philadelphia's Office of Emergency Management now includes Red Paw when it's responding to a large-scale crisis. In November, Leary and Albright appeared on a special edition of the Rachael Ray Show recognizing community do-gooders.
Leary has her eye on creating a chapter in Camden and eventually spreading throughout Camden County, then possibly setting up shop in Delaware.
Right now, however, her organization barely has enough money and resources to support the current operation.
And she has to get through this crazy winter.
"We just continue to get busier," Leary said.
At the wheel of "RP1," a mid-'90s Dodge Durango emblazoned with the Red Paw logo, the slender-framed, 5-feet-5-inch Leary arrived at a house in the 1500 block of North Ninth Street on a Saturday afternoon in December to pick up DJ, a pit bull.
The house next door went up in flames the night before, and DJ's house suffered severe smoke and water damage. His owners, a couple with two small boys, could not take the dog with them while they tried to recover.
DJ was not neutered.
"We can only hold him for 72 hours unneutered," Leary told the couple in their living room. "Everything is free, so you might as well get it done."
The couple agreed.
"We're going to get him checked by a vet, vaccinate him. Everything is free," Leary reassured the couple.
The following month, DJ was returned to his owners after staying three weeks with Jocelyn Tusavitz and Valerie Mitchell in Royersford, Montgomery County.
Tusavitz said she saw DJ on Red Paw's Facebook page and applied to be a foster. Virtually everything that Red Paw does is meticulously documented by Leary on social media.
The Red Paw page on Facebook has more than 14,500 followers, and is good for getting people to donate money and volunteer to foster displaced pets. Twitter, where Red Paw has nearly 2,600 followers, connects Leary with the news media.
Albright, who has a bachelor's degree in urban studies with a focus on nonprofit management from the University of Pennsylvania, is focused on obtaining grants.
"I'm not good at asking people for money," Leary said. "I'm very much boots-on-the-ground oriented."
Red Paw has built a network of 200 volunteers, including all of the people who foster, but they are all part-time.
"Full-time, actually committed to responding," Leary said, "it's just me."
Leary grew up in Olney and Northeast Philadelphia and attended Northeast High School with her identical twin sister, Marion, her only sibling.
"We graduated when we were 17 and moved right into the city, literally like the day after we graduated" in 1995, she said.
The twins once played professional full-contact women's football, including with the Philadelphia Liberty Belles in 2001. That year, she met Albright at an Eagles preseason game.
Marion Leary is now assistant director of clinical research for the Center for Resuscitation Science at the Hospital of the University of Pennsylvania.
Jen Leary joined the Philadelphia Fire Department in 2007.
"I always wanted to be a firefighter as far back as I can remember. I don't know why. I just did," she said.
In her academy class of more than 80 candidates, there were only three women including Leary, and two graduated.
Leary was assigned to Engine 20 in Chinatown, where it was again mostly men, but she got along, she said. "The guys were like my brothers."
In 2012, she suffered the dog-bite injury that, despite three surgeries, left her unable to close her hand to grip things, and that disqualified her from actual firefighting.
She decided to make Red Paw her life.
On a late Sunday afternoon last month, Leary visited with her sister in Northern Liberties, then went next door to where Geo was being fostered. There, she met Lt. Stephen Paslawski, the firefighter who came to the foster home to adopt Geo.
Paslawski made news when he adopted Campbell, a cat that was set on fire by two young men in November.
"He's such a good boy," Leary said as she got ready to say goodbye to Geo.
"I love that you're adopting him," she said. "I love that he's going to a firefighter. I love it."