What is the correct Islamic legal position and what advice is directed to someone who knows that a girl was born from an illegitimate relationship and is attributed to a sterile man who is not her biological father, and she intends to marry, knowing that more than one person is aware of this fact?

Legally, a girl is considered the daughter of a man as long as she was born on his marriage bed and he has not disavowed her through li'an (oath of condemnation), based on the Prophet's (PBUH) saying: "The child is for the bed." He is her legal father and is responsible for arranging her marriage. He is permitted to appoint someone else as his proxy. However, she cannot act as her own proxy in her marriage. It is impermissible to spread rumors that she is a product of zina (fornication/adultery), as this constitutes qadhf (slander). If it is proven that men enter her house in her husband's absence, she must be advised and threatened with informing her husband if she does not desist.