Marissa Flores was one of three children given a tour of the USS Enterprise-D by Captain Jean-Luc Picard in 2368 as a reward for the best science projects at that year's science fair. She was the oldest of the children, but was incredibly shy.
The tour was cut short when the Enterprise-D was severely damaged by a quantum filament. An injured Picard and the children were trapped and isolated in a non-functioning turbolift. In an effort to keep the younger children optimistic while they searched for a way out of the damaged section, Picard made Marissa his Number One. An emboldened Marissa responded well and helped to get the children to safety.
Marissa was played by actress Erika Flores.
Her last name was not given in dialogue, but was seen on the commemorative plaque given to Picard at the end of the episode.
According to the short story Morning Bells Are Ringing her father is a lieutenant named Peter Flores. Her mother is a professor named Elista Roth.