Novato, California (CNN) -- When health care reform passed Congress more than two years ago, Julie Walters yelled for her husband to come into the living room where she was watching the vote live on television.
"I was so happy," Walters remembers. "I yelled for Matt. I said, 'Do you know what this means? Do you know what this means?'"
The historic vote meant their 18-month-old daughter, Violet McManus, would be able to keep her health insurance. Without health care reform, she would have gotten kicked off her parents' insurance, perhaps as early as her 5th birthday, because her care is so expensive.
"I was like, Violet's covered now!" Walters remembers. "We're okay. We can breathe."
But now Violet's parents are worried they won't be able to breathe easily again.
This week, the Supreme Court is hearing a debate on health care reform. The court could keep the reform intact, repeal parts of it, or get rid of the law altogether.
"I'm really scared," Walters says. "Like, I-can't-sleep scared."
'Completely blue in her crib'
Violet McManus was born healthy, but when she was 11 months old her parents woke up in the middle of the night in their Novato, California, home to find her having a seizure.
"She was completely blue in her crib and shaking," Walters remembers.
It was to be the first of hundreds of seizures -- sometimes thirty in one day.
Violet has been hospitalized about six times and each hospitalization cost more than $50,000.
She's now on two drugs to control the seizures and carries oxygen with her wherever she goes because she stops breathing when she has her seizures. She needs speech therapy and frequent doctor's visits.
Matt McManus, Violet's father, gets health insurance through his work as a video game designer. Before health care reform, there was a $5 million lifetime limit on Violet's insurance policy. Violet is now 3 and her parents calculate she could hit that cap by her 5th birthday, and almost certainly by her 10th.
Health care reform made lifetime limits illegal -- which is why Violet's family breathed easier when it passed -- but now her parents are worried the Supreme Court could restore the limits and Violet would lose her insurance. Walters has been so passionate about health care reform she contacted the office of Sen. Barbara Boxer (D-California) and MomsRising.org to advocate for the law.
If Violet does lose her current insurance, her parents know there's no way another insurance company will want to insure her because her care is so expensive.
"They'd be crazy to want to insure her," Walters says. "I mean, I wouldn't want to insure her if I was an insurance company."
Watching the Supreme Court case closely
Several provisions of health care reform have already gone into effect, so millions of other people, like Violet McManus, stand to lose a lot if all or part of it is reversed.
For example, 2.5 million young Americans get to stay on their parents' insurance until their 26th birthday because of health care reform, according to the Obama administration.
Seniors and people with disabilities have saved $3.2 billion on prescription drugs because of health care reform and insurance companies and 45 million women have received free mammograms and pap smears because of health care reform.
There are ripple effects, too.
After health care reform passed, Walters and McManus felt more secure about Violet's future and decided to have another child. Violet's little brother, Rory, was born two weeks ago.
Violet's parents know not everyone shares their enthusiasm about health care reform. Some people even traveled to Washington to protest in front of the Supreme Court this week. In particular, they object to the "individual mandate," which requires nearly all Americans to purchase insurance or pay a fine.
The protesters object to being forced to pay for something they don't want, but Walters and McManus see it differently.
At any point in time they say someone could find themselves in a difficult situation like they're in now and would want a system that insures you no matter how sick you are.
As McManus puts it, "I think people just sort of need to change their mindset about health care."
CNN's John Bonifield and William Hudson contributed to this report.