"I thought at first glance that Dierdre had somehow returned from the Abyss, that she had climbed out and came back to me. She had Deirdre's eyes of blue and hair of black, though it was longer, down to the bottom of her shoulderblades, and the style different. You'd hardly expect her to have found a hairdresser in the Abyss. The clothing was different too, evoking memories of my time in America after the Civil War and before I returned to France to fight the Prussians. If Deirdre had been born in the Old West, this could have been her, complete with a brown leather gun belt, a battered black hat with silver trim, a black vest, a silver rose where you might expect a sheriff's badge to be, white buttoned shirt, and dark denim jeans over her brown leather boots. Then she spoke and my delusion ended. "Dad, where the HELL have you been?"
--Corwin's first meeting with Theresa
Theresa is generally believed to be a daughter of Corwin and Stacey Hawkins, a woman from Shadow Earth, born during his long amnesiac exile there. It can be generally guessed from how Theresa tends to dress and carry herself that they likely met during the time known as 'The Old West'.
Theresa first appeared shortly after the Patternfall war, stumbling into Arden with her mother, Stacy. She was nearly locked up by Julian, but convinced him to take her to Amber, where she successfully walked the Pattern. She spent a while in Amber, getting to know it, and spent a lot of time in the company of Bleys and Merlin. After Merlin vanished, she went out into shadow for years, looking for him, then returned to Amber and spent a while doing the 'drunk and morbid and bitter' thing.
Eventually, she got punched out by her mother at a formal dinner, snapped out of it, and went back out into shadow, where she seems to have been playing 'gunslinger errant' for the last twenty years or so. She has recently returned to Amber since her father's return, and seems to have spent a lot of time with him.
Theresa is a fair hand with a sword, but is most noted for carrying two pearl-handled Colt .45 Peacemakers with her everywhere unless forced not to. There's usually a rifle on her horse as well. This has lead to the occasional moment of embarrassment when she instinctively drew and fired at something and nothing happened.
Theresa is known to share her father's ethics of combat--whatever works, use it. She is more idealistic in other matters than him.
When drunk and morbid and bitter (rare these days, but...), Theresa has been known to moan and wail about Gilead. Whether it's a person or a place is unclear, but it's dead and gone, and apparently at the hands of Chaosians. While she got along well with Merlin, she is known to have no love for Chaosians.