The day started off with a ceremony on the steps of City Hall where she was greeted by Santa Claus and local dignitaries. The day was a surprise for Monika, she didn't know this was coming.
Her community already thinks she's a hero, but when the 10-year-old opened her front door at 8:30 a.m. she had no idea she was going to be a superhero for the day.
After a big surprise from a crowd that had gathered outside her home, she was whisked away. A police escort got her to Pennycook Elementary School where she was greeted by students waving signs and dressed up like their favorite superhero.
It was a lot for the 10-year-old to take in.
"I couldn't believe it," she said.
The kids even did a flash mob dance to celebrate their hero.
Monkia was diagnosed with leukemia in April. Her mom Alejandra Romo says she's now in remission and believes support like this makes her stronger.
"So, it's hard when a child is going through something like this when they know there are going to be changes in their body," she said. "And to have the support of the kids and the teachers you know, that's really helped her."
This was all the idea of the nonprofit group Vallejo Together. They wanted to do something special for a child suffering with cancer. It turns out Monika is the only child cancer patient in Vallejo.
"We asked if she needed a Disney princess theme or something," said Maria Guevara, founder of Vallejo Together. "But she doesn't like Disney princesses, she likes Wonder Girl. So we were like, oh my gosh, perfect setting, we're going to do Batkid-style Wonder Girl in Vallejo."
To trick Monika they told her she needed to write an essay for a contest about how a superhero could save Vallejo, a city that has struggled financially and against crime.
She read the essay to her school, proving that she really is a hero.
"Cancer is an evil villain attacking my body," said Monika. "It is similar in Vallejo, when Vallejo-ans are afraid to live their normal life. I choose to have a smile on my face."
Monika's strength and optimism served as an inspiration for many Vallejo residents.
"It's just very moving to see such a young girl with such a battle," Vallejo Assistant City Manager Michelle Straub said. "It makes out battles feel so small."
The day was a little different from Batkid's day. She didn't run around saving people from villains.
Monika wants to be a teacher when she grows up, so they focused on teaching. She went from school to school as an honorary teacher, finishing at the California Maritime Academy. She taught different groups from her essay about fighting villains from within.
In comic books, superheroes cure all evils, defeat all enemies, beat every long odd. In real life Monika showed that any of us can be a superhero, if we choose.
Wayne: "What was the lesson?"
Monika: "Never give up!"