Sarah's father was a police officer killed in the line of duty while trying to stop a robbery. From that moment Sarah and her siblings were raised by their mother, Fran Morgan, alone. Being the oldest child, she is very protective of her younger siblings, especially after the death of their father.
On Criminal Minds
Sarah visits her mother at Chicago for her birthday. There she is reunited with her brother who always takes time off to be there for Fran's birthday. When Morgan is arrested accused of murdering a young boy, Sarah is supportive of her brother, always believing in his innocence, which shows the closeness between the three siblings.
She reappears in this episode when it is discovered that her presumed-dead cousin is alive, having been held captive by Malcolm Ford. Sarah berates Morgan for telling the family a lie last year that Cindi was killed by an unsub operating in Jacksonville, Florida. When Cindi is brought home, safe and sound, with her son Anthony, Sarah embraces Morgan as thanks for bringing back their cousin and as a sign that she forgives him for the earlier lie.