Who is Amanda (Mandy) Starkey from Drowning Ruth and what is their importance?

Amanda (Mandy) Starkey is Ruth's maternal aunt who undertakes to raise her after her younger sister Mathilda (Starkey) Neumann's drowning, Amanda is tall, clumsy, awkward, and mentally unbalanced. She is proud of being a brilliant, popular nurse in a veteran's hospital, but realizes that she has lost control and returns home to recuperate. Amanda's symptoms are those of pregnancy (compounded by hallucinations), which months later results in the birth of a daughter whom she names Imogene and gives up for unofficial adoption to the Lindgrens on the night that Amanda delivers and Mathilda drowns.