Martha Kaply was a shy bookworm who got detention for objecting to participating in physical education. While in "JUMANJI", Spencer Gilpin tells her that he admired her from afar for some time and confessed that he likes her, and she admits that she also has feelings for him.
Martha is a bright student like Spencer, but had no interest in physical activities or boys. She was also shown to be judgmental and a bit arrogant as she openly, yet needlessly, called out the gym teacher for wasting her time with physical activities as she was more focused on schoolwork. She also dislikes like having tattoos on her body, because she revealed her mother would kill her if she got one.
Underneath this exterior, she was shown to be shy and lacked confidence in her abilities to be around boys, which she later admits to Bethany and was initially unable to confess her feelings for Spencer.
By the end of the film, Martha has lost her judgmental attitude, has gained confidence and started dating Spencer Gilpin.
Martha arrived back in their home town for Christmas from college where she'd become popular. She had been constantly messaging her at their friends, but it was only Spencer who would often not answer. He had even rain checked on her last two hangouts. After meeting everyone at Nora's, it quickly became clear Spencer wasn't going to show, despite having already confirmed he would. They all made their way to his mother's place, and after a quick introduction to his Grandfather, Eddie Gilpin, and his friend, Milo Walker, they all search the house. In the basement, they found the formally smashed up a Jumanji game console put back together. Martha admitted how Spencer had been acting, that he missed the feeling of being Dr. Smolder Bravestone. Martha and Bethany agreed they needed to follow Spencer into "JUMANJI" despite Fridge protesting the danger. It wasn't until after they were inside, she realized that Eddie and Milo were with them, Spencer was in another avatar, and that Bethany was missing. While scaling the cliffside leading up to Jurgen's mountain base, she and Spencer talk about Spencer's behavior. After hearing what was going on, Martha assured him that everything's okay. This results in the two kissing and reigniting their relationship.
As the film progresses, Spencer Gilpin began to have feelings for her and she has feelings for him. By the film's end, it is possible that they became a couple after they shared a kiss. She later called him her boyfriend as Spencer, as Bravestone, barged in before she started kicking the butts of Jurgen the Brutal's men at his fortress.