Abby Shapiro, 16, died last week from osteosarcoma, a form of bone cancer. (Courtesy of Shapiro family)

Abby Shapiro’s death can teach us one simple thing: The small ways you live your life every day are what matter.

Abby was just 16. And a really good swimmer. She thought Ethiopian food was “on fleek” (her favorite phrase to describe something awesome). And she did this hilarious Russian accent.

A pretty average 16-year-old, you’d think.

But when her parents started receiving hundreds of condolence e-mails and about 600 people showed up at her memorial service in Bethesda on Thursday — so many that people had to peer in through the windows of the Temple Adat Shalom — her impact on the world became a little clearer.

The hundreds of high school students gathered at her funeral? No one was talking about hair, clothes, make-up, Instagram selfies — the foundations of teendom. None of those things made people love Abby.

They loved her because she was real. And kind. And unfiltered.

“There were no mind games or BS or trivial fluff with her,” Isabel Brown, 17, said in a tribute to her. “She was just so genuinely and unforgivingly Abby.”

She died only months after a mundane nagging knee pain was diagnosed as osteosarcoma — a type of bone cancer — that quickly spread from her knee to her spine, throughout her central nervous system, to her lungs and to her brain.

In April, she started getting calls from college recruiters interested in having such a strong breastroker join their swim teams. About a month later, she was paralyzed and bed-ridden.

Her parents, Trudy Vincent and Rick Shapiro, went from making college plans for their only child to funeral plans in just five months.

It was a swift and slow-motion death all at once.

Her friends visited her in the hospital, kept her updated on their summers, talked college and senior year and Taylor Swift. The day they went back to school, doctors were telling Abby’s parents that they didn’t think she’d make it through the night.

Most teen deaths are far more sudden and violent — car accidents, drug overdoses, daredeviling, suicide. And kids grieve with rallies against drunken driving or with self-esteem seminars, counseling or peer support.

But this? What can anyone learn from the cruelty of this kind of rapacious, random and merciless cancer?

Abby’s own way of living. That’s what there is to learn here.

She was so utterly herself that she was infectious. She was loud, hungry, funny and in­cred­ibly brave. And because every person — her teachers, her doctors, her friends, her neighbors — had the same description, you also know that she was real.

The swim team members who spoke at her service didn’t say she was a naturally gifted, effortlessly winning swimmer. Because she wasn’t.

But she was dogged in her dedication. She got up at 4 a.m. to practice, then went to school, then got back in the pool to practice some more. She trained and trained, willing and sculpting her average, teen body into that of a champion swimmer.

The naturally gifted swimmers, those born with the broad, strong shoulders and paddle-sized hands, said they’d see her outpratice, outwork them. “She inspired us all,” one swimmer said.

And when she did break her own records, shatter her own walls, what did she do? She went around congratulating her teammates on their great times, not her own.

The way she lived her life in that pool was what people remember. Not her best times.

When her girl squad talked about boys, the advice Abby got was to tone things down, to be less raucous around boys. She did the exact opposite.

“In eighth grade, I taught a class that included a group of boys who seemed taken aback by the fact that Abby could, and would, stand her ground and give back at least as much as she received,” said Steve O’Keefe, one of Abby’s teachers at Edmund Burke School. “I don’t think the boys were prepared for her strength of character, feistiness and strong sense of self.”

There were few people, Rick Shapiro said, more ill-suited to face cancer than Abby.

As a young child, she watched her aunt’s long and painful death from breast cancer. After that, she was completely phobic about doctors, clinics, hospitals and needles. Even as a teenager, her parents had to sneak-surprise-kidnap her to the doctor for annual exams.

But on her deathbed? She was grace, strength and courage.

“She taught me what true bravery is,” said David Bushey, a Georgetown Medical School resident who was one of her doctors. “She was the strongest person I ever met.”

Throughout her chemo, her medication, experimental drugs, MRIs and paralysis, she was upbeat. She didn’t dwell, self-pity or depress.

Her nurses told me they’ve seen many children die, but none died like Abby.

“She took us into her squad, she trusted us. I’ve never seen someone treat everyone else like this before,” said Jamie Miller, one of Abby’s nurses. Every day, she’d ask each nurse and doctor about their boyfriends, their wives, their issues. She’d joke and laugh and put them at ease, as though she were the one in charge.

She never complained about the pain or the very fact that she was 16 and staring down death, her friends said.

While she was in the hospital, she stopped watching television. She said it wasn’t productive, her parents said. Instead, she made bracelets and art projects for her friends.

In those last days, when all her friends were getting ready to head back to school and she was paralyzed from the chest down and on a ventilator that put 60 pounds of pressure on her face to force air into her lungs, she insisted that her parents set up an independent study program for her. She didn’t want her grades to slip. Even though she clearly must have known her end was near.

Two days before she died, she was still trying to finish an art project that was a gift for a friend.

Her parents have a stack of eight or 10 gifts she made for them to hand out.

“One of the many lessons I learned from all this was that being who you are — being true to yourself — is what brings people to you,” said Sara Moss, 25, one of Abby’s close family friends. “We were all talking about this, about what people remember about you. And that was it. Being genuine. Being real. And kind.

“At 16, she had such an impact because of these basic things.”

Yes, a 16-year-old can have a legacy. And the one that Abby left behind is totally on fleek.