Martha Nielsen is the daughter of Ulrich and Katharina Nielsen, and the sister of Magnus and Mikkel Nielsen. She attends the Winden high school.
History
Martha had a romantic interest with Jonas Kahnwald earlier in 2019 but, during his extended absence from school, began dating his friend Bartosz, after Jonas return, she becomes torn between the two - something that, along with Mikkel's disappearance, causes her to become increasingly sorrowful.
She eventually calls and meets Jonas privately during the school play Martha is acting in. They talk about how both still have feelings for each other, Jonas confides in her that he was in psychiatric treatment instead of an exchange program in France (as Bartosz had told their classmates) and then kiss.
She later confronts Jonas personally after he apparently disappears for a few days. Now aware of his true parentage, Jonas rejects her succinctly, as there was no convincingly way to describe the impossibility of their relationship. Saddened and angered by Jonas' seemingly cold response, she reconciles with Bartosz after telling him about her meeting with Jonas.