A short synopsis on how Monica was introduced and received her powers below
Comic: The Amazing Spider-Man Vol 1 #16
Monica was born in New Orleans, Louisiana. She worked as a harbor patrol lieutenant. After being denied the promotion of captain, she gets a visit from professor Andre Leclare. He created a device that can tap energy from other universes, a project funded by the evil dictator Ernesto Ramirez. He asks her to stop the scientist working for Ramirez, Felipe Picario.
Monica manages to destroy the prototype with her bare hands, but is blasted away by the extra-dimensional energy from the device. She resigns and weeks later, she seeks the Avengers for help to rid her from the excess energy from the blast. Iron Man successfully conducts the energy away and Monica is saved. Dubbed Captain Marvel by the press, a powerful heroine was created.