Before the outbreak, Anna worked as a nurse and at some point became good friends with Marlene. Although they fought a lot due to Anna's stubbornness, they were close.
After the outbreak, she became pregnant and sometime during late 2018 or early 2019 she gave birth to her daughter, who she named Ellie. She died within a day of giving birth to her, but she had the time to write Ellie a letter. Before Anna died, Marlene promised to look after Ellie in her absence. She would keep her promise despite her position as leader of the Fireflies. After that, Marlene took care of Ellie for a while, but eventually put her in a military boarding school.
When Ellie was finally brought to Salt Lake City to reverse engineer a cordyceps brain infection vaccine, Marlene grudgingly gave the doctors the go-ahead to perform the surgery on Ellie. Knowing the operation will kill her friend's daughter, Marlene "speaks" to Anna and promises her that Ellie "will be with [her] soon."
Ellie carries Anna's letter with her in her backpack, as seen in the Winter chapter. At the end of the note, it is signed "Make me proud, Ellie!" and Ellie can be heard saying, "I'm trying to make you proud.."
Anna describes herself as being stubborn, tending to give people a hard time, and not liking children, especially infants. She also states in her letter to Ellie, that she knew she was going to die.