Marfa is the second eldest of the family, one year younger than Daniel. She is often dealing with her own teenage problems and is often in her room doing other things. She has less time to give Jacob advise than Daniel does since her older brother is more laid back and listens to their younger brother better.
Marfa knows that Jacob ruins everything that he touches, even though it's always an accident. She has a computer, which Jacob often has little success in using due to her paranoia that he might crash it because of Jacob's bad luck. Her personality changes based on her mood. For example: if she is angry, upset or stressed, she will be rude to Jacob and appear stuck up, conceited, and selfish as well as emotional. If she is happy, excited or calm, she'll be seen smiling and relaxed.
When Marfa was a child, she resembled her younger sister Emma with big bangs and her facial features.