COURTNEY SIMMONS always wanted to be an attorney. So she enrolled in Constitution High School, figuring its emphasis on history would give her a good grounding in the law.

Now a senior, she plans to be a pediatric nurse, instead.

Why the change?

"Things happened," she says.

How can I describe what happened to Courtney without making her seem pitiable? Especially when her classmates and teachers speak of her with awe?

"It's hard to imagine what this place will be like when she's off at college," says Constitution teacher Kathy Melville. "She's like the heart of this school."

Courtney's life got hard when she was 10, and her mom, Crystal, was diagnosed with cancer in her thigh. At 19, Crystal had also had breast cancer, but beat it.

Courtney's sister, Tina, then 15, stepped up in a big way to help their mother. She paid bills, shopped, fixed meals and looked out for Courtney and their little brother Reggie, then 8.

"I wanted to be just like Tina," says Courtney. "I never told her that. I wish I had."

Two years into Crystal's illness, the unthinkable happened: Tina got brain cancer.

Her doctors at Children's Hospital of Philadelphia suspected a hereditary cause, given Crystal's history. Genetic testing of the family yielded shattering news. Crystal, Tina and Courtney had Li-Fraumeni syndrome, a rare genetic disorder that increases cancer risk. Reggie had not inherited the syndrome.

Says Courtney: "I thought, 'OK, I'll probably get cancer one day.' But I didn't think much about it."

She had no time. She was now helping to care for her sister and mom, with help from a network of family, friends and teachers.

No doubt these people would have helped any child facing such a family crisis. But Courtney has always drawn people to her.

Like Debbie O'Donnell. Twelve years ago, O'Donnell met Courtney through Philadelphia Reads, which pairs elementary-school students with reading tutors.

"Courtney was wise beyond her years," recalls O'Donnell. "She had such an engaging personality and was very sure of herself. Those are traits you don't often see in a 6-year-old."

O'Donnell fell in love with Courtney (who calls O'Donnell her "godmom"), met the whole family and became close to Crystal.

"She was tough and sweet, and she put nothing before her children," says O'Donnell. "Together, they were this very tight unit."

Sadly, the family's love could not save Tina. She died in 2007, only a year after her diagnosis.

"It was intense," says Courtney, shaking her head. "That's the only way to describe it."

Over the next years, as Crystal's health wavered, Courtney focused on others, says her English teacher, Alison McCartney.

"There's not a single person in our school who does not know and love Courtney, because she actively takes the time to get to know everyone," McCartney says. "Even though she was facing unimaginable obstacles, she still cared about her friends' daily trials, always lent a hand."

By December 2011, Crystal was dying. Courtney wanted to stay home from school to care for her, but her mother refused.

"She felt so bad that Tina didn't live to finish school," says Courtney. "She said, 'Get your diploma. Go to college. That's what will make me happy.' "

Crystal died on Christmas night, 2011. Her funeral was on New Year's Day. Ten days later, Courtney was diagnosed with cancer.

Yes, you read that correctly.

"My knee had been hurting, but I thought it was from sports," says Courtney, who is athletic. "But then I started limping."

The diagnosis: osteosarcoma - bone cancer - in her left knee.

"I felt like I was in a Lifetime movie when the doctor told me," says Courtney. "It just didn't seem real."

Her only thoughts were for Reggie, now 16.

"If I died, he'd have no one," says Courtney, although by then they had moved in with a favorite cousin, Terry Jones, with whom they'd always been close. "I had to stay alive for [Reggie]."

Courtney underwent chemotherapy, surgery and brutal rehab while trying to keep up with schoolwork. Her teachers visited constantly, she Skyped into classes when she could, and a tutor at CHOP worked closely with her. But it was a grueling time.

"I watched my mom go through chemo, but you can't know how bad it is until you go through it yourself," she says. "You don't think you'll ever get better."

But she did get better and returned to Constitution in October, focused on a new career: pediatric oncology nursing.

"My nurses at CHOP took care of my health, my heart, my whole being," she said. "I want to help kids the way they helped me."

Last fall, she applied to area nursing schools (she must stay close to her CHOP docs) and was smitten by the program at Saint Joseph's University. On Christmas Eve, the day before the first anniversary of her mother's death, she was accepted into the school.

"It was the happiest day of my life!" she says, smiling broadly.

Courtney smiles all the time, says teacher Alison McCartney, who recommended her for the Philadelphia School District's Senior of the Month award.

"Courtney . . . has the unique ability of turning any obstacle into a positive," McCartney wrote in her nominating letter. "She is rejuvenated by her new chance at life . . . and she will continue to make this world a better place. She is the strongest, bravest and kindest person I know."

Such words make Courtney proud.

"All I want is to make people smile," she says. "It makes my heart sing."

Phone: 215-854-2217

On Twitter: @RonniePhilly