Given the following context:

In Fresno, California, optimistic Martha Jackson works as a housekeeper at a local hotel. Her older sister Shannon is a sex addict and frequently goes to rehab. Since Shannon has no job and needs to gain employment, Martha offers her a job as a housekeeper at the hotel.  As a celebration for Shannon's first day on the job, they go to a local bar.
After Shannon's celebration, Martha takes her back to her house and tells her where things are while she is away. However, she secretly sneaks off to her boyfriend Edwin's (Ron Livingston) house. Edwin is married but enjoys having an affair with Shannon. Meanwhile, Martha works out at the gym. Her trainer Kelly starts to take interest in her.
Next morning at the hotel, Shannon and Martha meet a guy named Boris, a slob who says that he knows everyone at the hotel. While taking a break, Shannon calls Edwin again. Edwin tells Shannon that he gave his wife a letter and had left her the minute she got it. Realizing that Edwin cannot go back to his wife, Shannon takes her anger out by going to Boris' room to have sex with him. Martha catches her in the act after she hears her scream in the distance. While Shannon defends herself from Boris, she accidentally kills him. Desperate to cover up the murder, they sneak Boris' corpse out of the hotel.
After sneaking out of the hotel, they take the corpse to Boris' family who has taken a disliking towards him. Shannon, posing as Boris' life guru, meets his sister Margaret. Margaret invites Shannon in to convince her parents that Boris has moved on in life and has left Fresno to never come back or to talk to his family again.

answer the following question:

What is the full name of the person whose sister is a sex addict? 

Martha Jackson