An Arizona girl who received a heart transplant at 18 months old is fighting again for her life after her body began rejecting the donor organ.

Jordan Drake, 5, complained of stomach pains last week, so her mother, Esther Gonzalez, took her to the hospital, according to 3TV in Phoenix. Doctors treating her found that her heart function was so poor that her life was in danger.

Jordan is now at Phoenix Children’s Hospital, hooked up to a machine that is performing her heart and lung function for her. Her poor heart function was also causing problems with her kidneys and liver.

Gonzalez told 3TV on Sunday that Jordan’s vital signs had shown some improvement, but that she still had a long road ahead.

"She's been really touch and go for a few days and on the fence, not knowing what would happen," Gonzalez said. "Just today, I was actually at church just in the past hour, her numbers have improved so much. She's doing great. We're going in the right direction."

A post Tuesday morning on Jordan's Facebook page, Jordan's Heart, indicated that her heart function was continuing to improve.

A GoFundMe page has been set up to help Jordan's mother with her medical expenses. As of Tuesday morning, the page had raised more than $4,800 of its $10,000 goal.

Jordan was born with a congenital heart defect that required a valve replacement, according to Jordan's Heart. While the replacement surgery was initially a success, blood clots that formed around the mechanical valve led to seizures and a stroke.

The toddler recovered from the stroke, but further complications led to bleeding on her brain and, ultimately, a heart aneurysm that required a transplant. The June 2013 transplant was a success, and she was healthy until last week.

Jordan’s story made national headlines last year after she met the mother of the 7-month-old boy whose heart she received. Jordan’s life was one of three saved by the donation of Lukas Clark’s organs.

Lukas' mother, Heather Clark, wept last January when she held a stethoscope to Jordan's chest and heard her son's beating heart once again. Jordan also gave Clark a special gift -- a Build-A-Bear stuffed bear covered with hearts and with a recording of Lukas' heartbeat inside.

The two families formed a special bond following that meeting. Clark posted a prayer request on Facebook after learning of Jordan's declining health, saying that "Lukas isn't ready for a new friend yet."

Lukas died June 21, 2013, three days after he stopped breathing while in the care of a babysitter. The San Bernardino Sun reported that charges were filed against the babysitter's boyfriend, Ryan Garcia, after law enforcement officials determined the boy had been abused.

Garcia, 25, of Ontario, California, is charged with murder and felony child abuse, the Sun reported. He remains in the San Bernardino County Jail in lieu of $1 million bond while awaiting trial.