Is a woman's repeated dream of a deceased person before their ritual washing, and her prior knowledge that she will be asked to wash a deceased woman, considered a cause for concern?

A righteous dream for a person who is upright in their faith is good tidings, and it is among the glad tidings. This is indicated by the Prophet’s (peace and blessings be upon him) saying: "Nothing remains of prophethood except the glad tidings." They said: "What are the glad tidings?" He said: "A righteous dream." And his saying: "If time draws near, the dream of a believer will hardly ever lie." Allah may inspire some of His servants with certain unseen matters, as happened to Umar ibn al-Khattab (may Allah be pleased with him). Indeed, what you mentioned about this woman regarding her trustworthiness, people's satisfaction with her, and the truthfulness of her inspiration and dreams, is an indicator of her righteousness, even though these matters may occur to those who are not upright. There is nothing in what you mentioned that causes concern as long as the person experiencing it is upright.