Teresa Goodwin is a woman that Marcus Jordan bumps into at an outside coffee cart after he finds out the old Chief of Police was killed. (What Lies Beneath). She was a photographer who shot ceremonies like weddings and school portraits.
Teresa and Marcus started dating after another run-in, and was only together a week before Teresa moves in with him because her roommate "Jen" kicked her out because her room mate's boyfriend was moving in and the lease was in her name (however, given her other deceptions this maybe a false claim). He offered to let her stay and she accepted. It was intended to be a temporary arrangement until she found a place of her own. Later she was questioned along with every outsider in the community at the time of the robberies as a matter of routine by the police in regards to a string of burglaries of Gates residences by Deputy Leigh Turner. Turner was suspicious due to Teresa's sketchy background including a lack of employment history. Marcus told her to back off that she was not connected to the robberies, particularly that the questionable items found in Teresa's car was Marcus's that he allowed her to carry. As it turned out, she wasn't. (Breach)
She found out a week later that Nick Monohan was going to attend the 5th Annual Father-Daughter Dance from her boyfriend Marcus. She offered to be the official photographer for the event for free. At the dance she photographed among others Nick, his daughter Dana, her friend Emily and her father Dylan Radcliff. She eventually got Nick alone. She then abducted him at gun point and force marched him into the woods. She tells him that her real name is Amanda Wolcott and she is the sister of the man that Nick Monohan killed. She just used Marcus to get inside The Gates and intended to murder Nick and his family. She had intended to kill his family first, beginning with his son, then daughter and then his wife and save him for last after suffering the stripping of his family from him like he did to her. However, she couldn't pass up the chance to catch Nick off guard, alone and unarmed. When she was about to shot Nick she is killed by Dylan Radcliff. (The Monster Within)
That same morning at dawn Dylan dug a shallow grave and buried her to hide the body. After a period of time Marcus grew concerned over her disappearance after repeatedly trying to call her and only getting voice mail. After defying Chief Monohan's orders and investigating her disappearance including interviewing Dylan Radcliff (who came up with a ersatz alibi), Marcus discovered Teresa's real name and deduced the real reason she came to town and befriended him. Feeling guilty for letting himself be used to potentially hurt the Chief, Marcus dropped the case.
Frank Buckley has a DVD recording of her being killed.(Repercussions) He later uses it to blackmail Nick into staying at The Gates.(Jurisdiction ) But later after Nick saves his life he drops out and presumibly destroys the tape.(Digging the Dirt)
After three weeks of nightmares of what happened the night Teresa died, Nick started to see her ghost around The Gates. Her spirit had been summoned by Devon after Sarah had stashed something underneath his pillow (which Sarah had thought would end his nightmares, except it actually taken images of his nightmare and shown them to Devon after she drank from it). Spirts sometimes linger, according to Peg, because they have unresolved issues, which in the case of Teresa was to revenge her brother's death. After almost drowning Charlie and possessing Sarah, Teresa in Sarah's body shot Leigh Turner and requested Nick to kill himself. Nick agreed to do it, and took her out to the swamp area where she was buried. However before he could shoot himself, he relieved all the built up regrets and apologizes for killing her brother. To his surprise, Teresa left Sarah's body - having exactly what she needed to move on.(Surfacing)
*Note: Date of death in infobox derived from the date of the text messages Charlie Monohan received from Andie on the evening of Chief Monohan's official welcoming party the next evening after Teresa/Amanda's early morning death the same day. (Repercussions)
She seemed a nice and clumsy woman but it was a facade. How she was before Nick killed her brother is unknown she could have always had this vengeful personality but it is also conceivable the trauma of having her brother killed and seeing his killer only leave the police force as punishment (in her mind) could had changed her. In either case and whether or not her brother was innocent is open to debate but she wanted revenge, but not only revenge in killing the man that murdered her brother but his family as well displaying an uncalled for viciousness.
But after Nick apologises to her and willingly accepts to die to protect his family Amanda is finally capable of forgiven him and move on to the afterlife.