Is it forbidden to conceal the existence of illegitimate siblings if the intention is to avoid shaming the mother?

Children are attributed to the husband if the marriage bed is established, based on the saying of the Prophet, peace be upon him: "The child belongs to the bed." It is not permissible to attribute them to anyone other than the father unless the husband denies paternity and performs li'an (oath of condemnation). If a daughter sees her mother committing indecency, then concealing it and advising the mother to repent is obligatory. If it is merely a suspicion, then the daughter must repent for her ill-conjecture.