Seven-year-old Amillian Villa just got a new bike — and a new arm so she can ride it.

The Bronx girl, known as Mimi, suffered a heartbreaking amputation of her left arm after she was stricken with flesh-eating bacteria just as she started kindergarten in late 2017.

An initial misdiagnosis nearly killed her — emergency-room doctors failed to detect the often life-threatening infection and sent her home. It then spread rapidly, causing multi-organ failure.

Even after surgeons had to remove Mimi’s arm, they feared she could die, lose another limb or suffer brain damage.

“There was nothing I could do but get down on my knees and pray,” said her mom, Vanessa Avila. “It was a nightmare.”

During the past 19 months, Mimi has struggled to recover her health as well as her self-confidence and independence.

But she’s mastered everything from tying her shoes to dribbling a basketball.

“Mimi can do anything a two-handed person can do — she just does it differently,” said Kelly Milano, her occupational therapist at Blythedale Children’s Hospital in Valhalla, where Mimi learned to adjust to her amputation and now attends school.

“She doesn’t want to ask for help. She wants to do it herself.“

Mimi was fitted with a prosthetic arm last week, then got the bike, a gift from Handspring, the Middletown, N.Y., company that devised her prosthetic.

During a visit from The Post, Mimi hopped on the bike and started riding it, her mom helping steer.

But she will soon get an attachable device for the prosthetic to grip the handlebars, so she can go solo.

Mimi also received “A Doll Like Me” with brown hair, brown eyes, and one arm.

A 9-year-old Wisconsin boy, Rylan Ernst, raised money at his birthday party to donate the doll, which was hand-made by Amy Jandrisevits of Milwaukee.

Her small non-profit crafts dolls for kids with disabilities or those undergoing medical treatment.

“I named her Precious and she looks just like me,” said Mimi, who sleeps with the cuddly doll.

“It helped lift Mimi’s spirits,” Milano said. “When Mimi first came to us, she was very traumatized by everything she’d been through.”

It’s a mystery how Mimi contracted the disease, her doctors say.

She complained of pain in her arm while at school in November 2017, a few days after she went to a hotel swimming pool for a party. But she had no cuts or scrapes that could be infected, her mother said.

The next morning she woke up with a fever, and her mom took her to the emergency room at St. John’s Riverside Hospital in Yonkers, where they lived at the time.

The ER’s X-rays showed no broken bones. “They thought it was a sprain,” Vanessa said.

After checking Mimi’s ears, nose and throat, she added, the doctors attributed her temperature to a common cold.

“They just sent me home, and told me to give her Tylenol and Motrin for the fever and pain,” she said.

Two days later, Mimi’s arm was severely swollen, “hard as a rock,” and turning purple, her mom recalled.

She took Mimi back to the ER. This time, the doctors did an ultrasound and more X-rays.

They concluded it was a possible blood clot that needed to be drained, she said, and sent Mimi by ambulance to Westchester Medical Center for the procedure.

Once there, she said, “Right away, the doctors looked at me and said, “This is not an injury. It’s a serious infection.”

Mimi was in septic shock.

Tests confirmed the presence of group A Streptococcus bacteria, the most common cause of the flesh-eating disease.

About 700 to 1,200 cases due to these germs occur each year in the US — “and we believe this is likely an underestimate,” said Kristin Nordlund, a spokeswoman for the Centers for Disease Control and Prevention.

In other cases, when people expose an open wound to saltwater, the vibrio vulnificus bacteria — which is not usually found in “properly maintained, treated” swimming pools — can trigger it, Nordlund said.

The Westchester doctors tried to save Mimi’s arm by removing dead skin, but the infection spread so rapidly they had to amputate.

Mimi was hospitalized for three months to recuperate from injuries to her kidneys, liver, respiratory system and brain.

But she was lucky. “She arrived just in time to save her life,” said Dr. Kathy Silverman, Mimi’s pediatrician at Blythedale.

After surgery, Mimi was so weak she could not stand up or walk for months. She spent three months as an in-patient at Blythedale.

Miraculously, Mimi has since blossomed into the joyful child she was before her illness.

She loves to sing, dance, do artwork, and pose for pictures. “I want to be a model and a veterinarian,” she said.

Her proud big sister, Ashanti, 9, said, “She can make a peanut butter and jelly sandwich by herself. She can’t pour cereal by herself — that’s the one thing she needs to improve on. But she can do most things by herself without any help. She’s very independent.”

Mimi’s story should serve as a warning to parents, Dr. Silverman said: “If your child has what looks like an infection in their skin — red, swollen and tender — it needs to be seen by a professional. That area can spread and enlarge quickly, within minutes to hours.”

In 2005, a 10-year-old Bronx girl died from the disease.

In her case also, doctors at first thought she had a cold, The Post reported at the time. Then her hands began to swell, and she was sent to Montefiore Hospital, but it was too late to save her.

The NYC and New York state health departments could not say how many residents have been afflicted with the flesh-eating disease.

A St. John’s spokeswoman said the hospital will look into its treatment of Mimi.