Marsha Bruenig is one of the child Townies in The Sims 2. She can be found in Pleasantview, which ships with The Sims 2, and in custom neighborhoods. She can be aged to the Teen life stage along with any playable child Sim with the FreeTime expansion pack.
She is sometimes considered annoying, because a glitch in the older EPs had her calling Sims she knows on the phone all the time, even at night time and during school time. This is referred to as "phone-stalking". Marsha may even phone-stalk Sims she has only met once and has only a 0/0 (or lower!) relationship with.
It's implied that Marsha is an orphan, because if a family adopts a child, it is sometimes her. She will still be named Marsha, but she'll have the last name of her new parent/s, and her new family will appear on her tree. Adopting or growing her up to teen with the FreeTime expansion pack and then sending her to college if University is installed will stop this strange behaviour.