Warning: The following contains spoilers for later books. Read at your own risk.
Susan Rodriguez, a reporter for The Midwestern Arcane and Harry Dresden's long-running girlfriend, covering supernatural type events for the tabloid. She was able to get most of her information from Harry on things he'd become involved with, though he was a willing informant. Their relationship became more involved in "Fool Moon" and lasted until Susan was captured by Bianca in "Grave Peril" and changed into a half-Vampire, though their love for one another remained strong.
Harry tried to find a way to help Susan return to her former self, without success because of his love for her. In fact, Harry had always had trouble saying "I love you" to any woman until during a time of "bloodlust" he said it to Susan in hopes of bringing her out of it. Susan Rodriguez was the one woman who Harry had said "I Love You" to in the Dresden Files. After that, he found it easier to say to her, though after proposing to her, she ended up leaving him shortly after leaving them both in pain. She knew marrying him would only endanger his life with what Bianca had turned her into, and she couldn't do that to him.
Death Masks; Pg. 309
"As I watched over the next few moments they vanished completely.
"I love you," she whispered.
"I love you."
Death Masks; Pg. 311
I watched her face, graced by pale candlelight, until my eyes closed.
She was so lovely.
I wished that she were with me.
Susan is an agent for the fellowship of Saint Giles, mother to Harry's daughter, Margaret Angelica, named after Harry's mother. Conceived apparently during "Death Masks", Maggie has dark eyes and hair. Susan kept Maggie secret to protect her because she felt Harry's life too dangerous and put her a place she thought would be safe for her. However when he found out after a surprise call which is the begins "Changes" with Susan telling him that their daughter had been taken, he was furious. During Changes, however, Harry forgave her for not telling him.
In the end, Susan was sacrificed for her daughter, for Harry, for all is the ultimate, though Harry actually did the sacrifice and Susan allowed it doing more than she ever ended up realizing in Changes.
Susan Rodriguez first appeared in "Storm Front" and subsequently in "Fool Moon", "Grave Peril", "Death Masks", and "Changes". She appeared in one episode of the television series based on the books, the episode entitled "Storm Front" and was portrayed by Rebecca McFarland where the character is blonde instead of the darkhaired character in the book.
STORM FRONT - Susan introduced.
FOOL MOON - Harry starts dating Susan Rodriguez and their love grows.
GRAVE PERIL - Susan is attacked by Bianca of the Red Court after copying an invitation Harry had gotten to a ball Bianca has. Harry proposes to Susan, but she turns him down and leaves for South America for his own protection.
DEATH MASKS - Susan returns to speak to Harry, letting him know that she and Martin have not been "involved" with one another. It is during this time that she and Harry conceive their daughter before she returns to South America with Martin.
CHANGES - It is during this time that Harry receives a call from Susan and she reveals to him that their daughter, Margaret Angelica has been kidnapped.