However, her symptoms continued to get worse over the next couple of days, so Rylie's parents brought her to the emergency room for testing.
"She was just moaning, laying there," her father Nate Whitten tells PEOPLE. "That's when I realized something's definitely wrong."
Rylie tested negative for influenza and spinal meningitis, but a blood test showed that she had a major infection and kidney malfunction. She was immediately transported by helicopter to Helen DeVos Children's Hospital, where it was determined she was suffering from toxic shock syndrome resulting from her use of a high-absorbency tampon – even though she was using it properly.
"It took over all of her major organs and shut them down," says Nate, 37.
The extremely rare disease can cause organ damage, shock and even death in 50 percent of cases. Toxic shock syndrome occurs in only 1 out of every 100,000 people, and is caused by complications of a bacterial infection. Symptoms include sudden high fever, low blood pressure, vomiting, diarrhea, rash, confusion, muscle aches, redness of the eyes, mouth and throat, seizures and headaches.
"We're so lucky we caught it when we did, otherwise she wouldn't be with us," says Nate.
Fortunately, Rylie is expected to make a full recovery – but it wasn't easy getting to this point. She spent much of her hospital stay on life support.
"Right now she's completely off the ventilator – she's breathing on her own – and her heart is beating on its own," says Nate. "She has a case of pneumonia and her vocal cords are a little damaged just from being on the ventilator for so long, but she's just starting to talk a little bit. The biggest sigh of relief is that she's mentally there."
Still, there is a long road ahead, including intensive physical and occupational therapy.
RELATED VIDEO: 'I Wanted to Kill Myself': Heartbroken Model Loses Leg to Toxic Shock Syndrome after Using a Tampon
"It's been a rollercoaster ride," says Nate of how he has coped over the past two weeks. "Some days you just lose it for no reason. At this point I've got a huge sigh of relief; at the same time, I think reality's setting in about how many times we almost lost our daughter."
Nate credits the outpouring of support from his local community of Greenville, Michigan, with helping him and his wife Jill make it through their difficult time.
"The amount of support that we've had is just insane," says Nate. "I think I've cried just as many happy tears and amazed tears as we have sad tears dealing with this situation."
In addition to setting up a Prayers for Rylie Facebook page, members of the community have held a prayer vigil for Rylie in their local church, and a half-time show at her high school, where she is a member of the dance team, was dedicated to her.
"The whole crowd was chanting her name," says Nate. "Every restaurant in town has 'Pray for Rylie' on their signs. That stuff, you don't know how to respond to other than cry. It helps. I'm so thankful for it."
Model Lauren Wasser, who was forced to have her leg amputated after suffering from toxic shock syndrome caused by a tampon, also shared her support.
"My heart breaks for this little girl and her family," she told PEOPLE in a statement. "This is why I have been so vocal about my experience. [Toxic Shock Syndrome] is real."
Nate hopes that Rylie's experience can motivate others to learn about toxic shock syndrome's symptoms and risks.
"Educate yourself," he says. "Take 10 minutes and read about it. Be aware of it."
With reporting by ANA CALDERONE