Who is Zilpha Marsh from Spoon River Anthology and what is their importance?

Zilpha Marsh tells the reader she was a medium in her life in Spoon River, who saw many spirits and spoke often of occultish subjects. The townspeople accused her of talking nonsense, she tells the reader. For her defense against that charge, she tells the reader that speaking to the people of Spoon River was like speaking to spiritual children: when one speaks to children, one must needs speak nonsense.