Who is Roswitha Gellenhagen from Effi Briest and what is their importance?

Roswitha Gellenhagen, a native of Eichsfeld, finds herself in Kessin serving the widow Rode, who dies soon after. Her grief seems to be the only sincere display of emotion at the widow's funeral. When Effi finds her sitting beside the fresh grave, she learns that the widow's penny-pinching relatives have hardly given her enough money to return to Berlin, and she intends to sit in the cemetery until she dies. Effi has a good feeling about Roswitha, and she hires her to be nurse to the baby she is expecting.