"You can tell that she wants to play soccer but she can't. Now that she has her heart, she can," said her big sister, Shayde.
Shayde is 9 and knows a bit about what Emily is going through. She has the very same condition, called restrictive cardiomyopathy, in which the heart doesn't relax as it should between pumps, so it doesn't properly fill with blood.
"Less than 1 in a million are diagnosed with this type of heart disease," Dr. Kristine Guleserian of Children's Medical Center in Dallas told CBS News correspondent Hari Sreenivasen. "To have two family members, it is even more rare. To have two sisters with it who are so close in age is incredibly rare."
A transplant is the only cure. If left untreated, this heart disease can bring on a sudden heart attack or even death - every parent's worst nightmare.
"You hear a loud thud and you go running, or if one of them starts screaming 'Mommy! Mommy!' your heart sinks, you go into panic mode of what just happened," said the girls' mother, Natalie Van Noy.
Emily waited 9 months for a donor heart, while Shayde is still waiting for hers. The transplant surgery took doctors five hours.
On CBS' The Early Show, Van Noy said that the wait for a donor heart for Emily has been extremely difficult.
"We've been in pretty much panic mode, waiting on a new heart. We were told after the first year, it was 50/50 on the survival rate. It's been hard."
"Well, the waiting, it's torture, no doubt," Van Noy said. "But as far as anything different we do, we pretty much keep on the status quo and keep to our daily lives. We want the girls to feel like they have normal lives and want to keep it good that way."
The girls' father Matt Smith told Smith that he immediately noticed changes in Emily after she received her new heart.
"Well, the immediate difference is her colors," he said. "Her lips are vibrant red. And her hands and feet stay warm which is a situation that was never the case before. I mean, there's already such a marked improvement, and we're pretty excited about that."
Her parents expect her to be able to leave the hospital on Tuesday or Wednesday.
Shayde is looking forward to the day her mom can stop worrying, and her life can get back to normal.
"When I do my surgery, I'm gonna do gymnastics, then go to cheerleading," she said.
Van Noy said the idea of being able to have the girls' dreams of gymnastics and cheerleading come true makes the wait worthwhile.
"Oh, it definitely is, it definitely is. It will be a big relief to know that they can go out in the backyard or go over to a friend's house and I don't have to constantly worry or send medication or, you know, all of that kind of stuff. It will be a big relief."
Smith asked Shayde how it was for her having to wait for a new heart.
"Hard," she said.