Is it permissible to donate an apartment to settle an unlawfully acquired financial debt, and does she bear a sin for that, and what about the rights of the heirs and informing the husband?

You must immediately dispose of the apartment because it is not your property, and this should not be delayed until death. Money taken unlawfully must be returned to its owners if they can be reached. Otherwise, it should be given as charity on their behalf. If even that is not possible, then you must increase your good deeds and humbly supplicate to Allah to make them pleased with you on the Day of Judgment. If you cannot reach the rightful owners, then give as charity on their behalf the amount of money you took. If the apartment represents the value of this money and you own nothing else to give as charity, then give the apartment as charity on their behalf. It is permissible for someone who possesses unlawful money to give it as charity to themselves and their dependents if they are poor.