Nia Wilson Had Big Plans. Then She Was Killed in a BART Station.

Nia Wilson was the youngest of six sisters and two brothers, but she knew how to stand out.

She jumped at the chance to help others, one of her sisters said, offering pep talks to her sisters when they were down and performing the Heimlich maneuver on her aunt as she was choking at a recent family party. She loved to look pretty, the sister said, even if it meant holding up everyone else until she picked out the perfect outfit for a late-night run to the grocery store.

At 18, Nia still had the bulk of her life ahead her and she had big plans — joining the Army or becoming a paramedic, or maybe a music producer would see her rap videos on YouTube and offer a record deal. But on Sunday night, Nia was attacked and killed by a man with a knife after stepping off a train with two of her sisters at an Oakland, California, transit station. One of her sisters, Lahtifa Wilson, 26, was also stabbed. She was taken to a hospital but later released.

Three days after Nia’s death, her sister Malika Harris said that her family was struggling to process what had happened and to accept that she was gone. In any other situation, her sister said, they would be turning to Nia for comfort.

“She was always there and motivating you and telling you to stay positive,” Harris, who was not with her on the train, said in an interview Wednesday.

As her family finalized funeral plans for Nia, the man accused of stabbing her, John Lee Cowell, was formally charged with murder and attempted murder. Cowell, 27, made his first appearance in an Oakland court at an arraignment hearing Wednesday afternoon. He did not enter a plea.

Nia’s father, Ansar Muhammad, went to the courthouse to attend the hearing.

“My daughter was everything to me,” Muhammad told reporters outside a courtroom. “She was so beautiful, so inspirational, had dreams. I’m supposed to be planning her graduation, not her funeral.”

The Bay Area Rapid Transit police arrested Cowell, who they said was homeless and had a lengthy criminal record, on Monday evening after a nearly 24-hour citywide manhunt. His family released a statement to a local TV station that said Cowell was given a diagnosis of bipolar disorder and schizophrenia, and had not received recent proper mental health treatment.

Harris said she believed that the fatal attack on Nia, who is black, should be classified as a hate crime. “They are trying to say that he was sick and crazy,” she said. “It was an act of racism.”

After the arrest on Monday of Cowell, who is white, the police said that they were still searching for a motive and had not ruled out race as a factor.

Images from local news media show sizable crowds at a vigil Monday evening for Nia at the MacArthur BART station in Oakland, where the stabbing occurred. For Nia, Sunday was the start of what was expected to be an emotional but exciting week, Harris said.

That afternoon, she traveled with some family members, including several sisters, from Oakland to her aunt’s apartment in the nearby city of Concord. Her aunt has Stage 4 cancer, so the family organized a pool party and cookout to celebrate her life.

At the party, Nia posted some video footage on social media. Only 49 seconds long, it still captured so much about Nia, her family said.

She can be seen posing for the camera, wearing a gold necklace and sparkly pink eye makeup, pausing to hug family members or to direct a comment offscreen.

“She wouldn’t go anywhere without looking presentable,” Harris, 25, said. “She was really passionate about the way she looked and carried herself.”

Nia had a job interview scheduled later in the week. For the past several months, Nia, who graduated from Oakland High School last year, had worked at a clothing distribution center for an online consignment store.

Harris said that Nia told her about the interview for the first time on Friday — but she refused to reveal much, not even the name of the place or the type of work. Harris said she pressed her sister for more details, but she would not budge.

“She wanted to keep it a surprise,” she said.

Nia was also planning to attend a party with friends for what would have been the 18th birthday of her high school boyfriend, Josiah Pratt-Rose. He and his best friend drowned in May 2016 after jumping off a boat in Woodward Reservoir near Modesto, California.

Not long after the boys died, Nia attended a vigil for them in downtown Oakland, Harris said. She was standing near a girl who had just performed a dance routine when someone fired a gun into the crowd. The girl, Reggin’a Jefferies, was hit in the neck and fell to the ground.

Bleeding and struggling to breathe, she asked Nia to stay by her side, Harris said, until the paramedics arrived and placed her in an ambulance. Nia stayed with her. Reggin’a was later pronounced dead at a hospital.

“Any way she could help,” Harris said, “she would be there for you.”