When Joseph and Shelly Balboa's daughter was 2 months old, the couple noticed some concerning symptoms The parents say they were brushed off by their first doctor, but kept pushing to get to the root of little Jayla's symptoms: namely weakness on her left side and shaking in her sleepYears later, they learned their youngest child had Rett syndrome, a rare neurological disorder. They've since shared their story publicly on Instagram and TikTok Everything had gone perfectly with Shelly Balboa's third pregnancy, and she and her partner, Joseph, were overjoyed when they welcomed their first daughter together, Jayla. But two months after Jayla's arrival, the California couple noticed something was off: the left side of their daughter's body seemed weak. Jayla wouldn't lift her left hand the way she did her right; her right pupil was significantly larger than the left; and she was shaking in her sleep. Concerned, Shelly and Joseph — also parents to sons Joseph Jr., 10, and Jacob, 8 — brought their worries to their doctor. "She said, 'Oh, Mom, she's fine. You act like she's your first child,' " Shelly tells PEOPLE exclusively. "I kept begging her, saying, 'Well, I noticed this, and I noticed that.' The doctor tried to make it seem like I was being a little dramatic, but I was an experienced mom." "I was like, 'No, this isn't right.' So luckily, I trusted my instincts and just kept pushing and pushing," Shelly continues.Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from celebrity news to compelling human interest stories. Eventually, the couple switched doctors. Jayla's new care team ordered an electroencephalogram (EEG), a test that measures the electrical activity in the brain. From the results, doctors concluded that the shakes in her sleep were seizures, and they decided to proceed with more genetic testing. Then, on Feb. 1, 2023, Jayla was diagnosed with Rett syndrome. "We were in the garage when I got that call, and the minute I answered, I had this feeling — 'Why are they calling me? They shouldn't be calling me.' I immediately knew something was wrong," Shelly recalls. "I took the call, and when they told me it was Rett syndrome, I remember it sounding familiar. I said, 'Don't tell me this is the one where the child loses skills, where it causes regression?' I'll never forget when they said, 'Unfortunately, it is.' " According to the Mayo Clinic , Rett syndrome is a rare genetic neurological and developmental disorder that affects the way the brain develops. While the symptoms can vary from person to person, it often causes a progressive loss of motor skills and language. Jayla, Shelly tells PEOPLE, she exhibits a range of symptoms, including breathing abnormalities, seizures and being nonverbal. By the time she was 1 year old, Jayla had lost her ability to speak. Due to the risk of sudden death from seizures, Shelly says someone must stay with Jayla at all times to ensure she's breathing. Car rides can be especially scary for Shelly; if Jayla starts holding her breath in the backseat while Shelly is driving, she has to pull over immediately. "You live in constant fear of not knowing," Shelly says. "You get used to the losses you've already experienced, but then a new problem arises, and you have to grieve all over again. But through all the dark days and painful moments of watching her regress — losing her speech, seeing her hands make repetitive movements — I think the light is in her smile. She can have a seizure, and then smile right after it." "We've been very honest with our other kids," she adds. "We tell them, 'If you see me crying, it's because I'm Mom, and it hurts. This is Jayla's diagnosis. We need everyone's help.' I believe this journey will make them better men in the future. They'll understand disabilities, and they'll know how to include children with special needs." Now, just more than a year after Jayla's diagnosis, she is 4 years old. Her parents have shared her story on TikTok and Instagram , where many of their videos have gone viral, garnering thousands of views and comments. Some of the videos showcase Jayla's day-to-day life, including attending daycare, doctors' appointments and various types of therapy from swimming to gymnastics. She has been in occupational therapy since she was 4 months old. "The biggest therapy that has been a life-changer for her is horse therapy," Shelly says. "We go to a local ranch called Heart of the Horse Ranch Therapy, here in Clovis, and it's magical to see. I don't know what it is about horses, but it helps her so much. She breathes normally while riding, and she's even said 'duck' while on the horse. She said it on the horse! There's just something therapeutic about the horse, and that's been the number-one game-changer for her. We just love that place because they've helped bring her back into their routine, and we're so grateful to them." Shelly adds, "I also think the key has been starting physical and occupational therapy at an early age. That's been huge for her development." Along with these videos, the family also shares educational content about Rett syndrome and their efforts to find a cure. They've also started a small business called "RETTY For a Cure!" where they collect donations for research organizations. "The only thing I can control is spreading awareness," Shelly says. "I want to make sure the world knows about Rett syndrome so that there will always be funding for research and to keep the science moving forward." "She's a sassy little girl, but she's so happy. I always tell people that we might be crying over here, but she doesn't care about Rett syndrome," Shelly adds. "She doesn't even know what Rett syndrome is. She just wants to have a good time. You can tell if she still had her voice, she'd be very chatty because she communicates in her own way — she talks with her hands, babbles and loves all things girly." "When I have my eyelashes and makeup done, she's like, 'Oh, hey, there you are! Where have you been?' She's very chatty in her own way — just so girly and bubbly," she adds. 
