Who is Liza Tillerman from Dicey's Song and what is their importance?

Liza Tillerman is Dicey's mother. In the previous book, Homecoming, Liza falls into a deep depression after her man leaves her and she loses her job. Liza wonders off one day and never looks back. Dicey and her siblings eventually learn that Liza is in a mental hospital in Boston. Liza has stopped eating and Dicey and her grandmother finally get a call that she is dying. They go to Boston and sit with her until her death, then bring her body back home to bury in the front yard.