Homeless Woman appears several times in Sons of Anarchy. Always when Gemma or Jax are going through an emotional decision making process.
In the episode 'John 8:32' it was stated that she may be Emily Putner, mother of Brooke Putner. Emily was accidentally killed as a result of John Teller's collision with a semi-truck and trailer in 1993.
In the same episode, when Jax goes to talk to Gary Putner about his daughter's aggressive behavior, he sees a wedding photo of Emily with Gary. When Gary asks Jax why he's curious about it, he states that "She looks familiar". Gary then says that he has also often seen her. He also tells Jax that he has had other people come to him saying that they have seen her too. This could mean that the Homeless Woman is actually Emily's ghost, but as of Season 6, this has not yet been proven.