Why does Helen focus her life of caring for Maude's needs in the novel, Lie Down in Darkness?

Maude was born with a congenital birth defect and as such, she is physically and developmentally impacted. Maudie requires a great deal of time and care, and her mother dotes on her because of her specific physical needs.

Note, this causes a great deal of resentment on Payton's part, and she too, needs attention.