September 18, 2014 04:38 PM

Judy Eddy/WENN

Olympic gold medal-winning gymnast Shannon Miller calls her 15-month-old daughter Sterling her “miracle baby.”

Miller was diagnosed with a rare form of ovarian cancer (her older child, son Rocco, was 1 at the time) and lost her left ovary and fallopian tube. But before Sterling was even a thought, the Olympian was going through chemo and speaking publicly about her diagnosis when a stranger changed her life.

“This woman came up to me and took my hand, right before I went on the podium, and said, ‘I just want you to know, I had the exact same tumor. That was 10 years ago. I have two beautiful children. And you’re going to make it,'” an emotional Miller told PEOPLE at the American Cancer Society Cancer Action Network‘s Cancer Lobby Day in Washington, D.C., Thursday.

“I don’t know that a day goes by that I don’t think of her. Every time I look at my daughter, I think of her. I hope I can be that voice that that hope for someone else.”

Miller, 37, who runs her own company, Shannon Miller Lifestyle, says the signs and symptoms of ovarian cancer include bloating, weight loss or weight gain and abdominal pain.

“I’m sorry, but what woman is going to rush in to the doctor and say, ‘Oh my God, I have ovarian cancer because I have a tummy ache?'” she says. “That’s why they call it the silent killer. We need to work very hard to raise funds so we can get that research so there will be some time of screening or exam.”

Now cancer-free for three years, Miller says she feels blessed to have two healthy children, and lights up while talking about their relationship.

“Rocco loves his baby sister and takes care of her,” she says. “There was a big clap of thunder the other day and here comes my son: ‘Baby girl! It’s okay!’ Of course, she could care less. But it was so sweet. And yes, ‘baby girl’ is what I call her because that’s what my son calls her. Or ‘sister bear.'”

The feeling is mutual between Rocco and his sister. “She loves her brother,” says Miller. “She just stares at him and wants to do anything he’s doing. She’s like a little infant tomboy – she likes planes, trains, dump trucks.”

Another favorite toy in the household? Mom’s collection of hardware.

“He’ll put on the gold medals and then hand me the silver,” Miller says with a laugh. “He does these one-mile fun runs and he makes me look online: Are they giving away medals or ribbons? Every now and then, he’ll [pick up one of mine and] say, ‘I won this medal.'” Which presents a perfect opportunity for Miller to teach her children the value of hard work.

“Sweetie? Let’s just be straight here. Mommy worked really hard for a lot of years for that. But you won this one over here!”

@pnp07 yes!! Miss you. He’s getting big and so is baby girl

— Shannon Miller (@shannonmiller96) September 6, 2014

— Rennie Dyball

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