I'm sorry, I don't know Sarah Jane Salazar personally, so I can't provide her life story specifically. But generally, a life story could include details like where she was born, her family background, her education, and her career path.
Yes, generally they are suitable for a wide range of ages. They often contain elements of adventure, mystery, and friendship which can be enjoyed by both kids and young adults.
Adventure is a major theme. The characters are constantly on exciting quests. Another theme is friendship, as the characters rely on each other. Mystery also plays a big part as they often have to solve strange phenomena.
Adventure is a very common theme. Given her character's history of traveling with the Doctor and having her own adventures, many fanfictions continue this trend, taking her on new and exciting missions. Another common theme is friendship, especially her relationships with the Doctor, her companions, and the friends she makes in her own series. It often explores the deep bonds she forms.
I'm not sure if Dr Sarah Harding from the Lost World novel was described as black. It could be that the focus of the story wasn't on her race, but on other aspects of her character and the plot.
Social media platforms can also be a source. Look for Doctor Who or Sarah Jane Smith fan groups on Facebook or Twitter. Some fans might post links to their fanfiction there or discuss where to find the best ones.
I'm not sure exactly who Sarah is without more information from the story. But she is likely a person who has a weight problem and is the focus of the '600 pound life' story.