What country are you in? What state? It makes a lot of difference. In most states of the USA, the wife does not automatically inherit the husband's real estate, unless she is on the deed of title. If she was never on the deed of title with him, and he has signed it over to his daughter, then when he dies the daughter will own it--actually, from what you say, she owns it already. I don't think the wife can do anything unless she was on the deed of title with her husband, and he somehow transferred the deed to his daughter without getting the wife's signature.
Under the laws of most US states, if a husband dies, his legal wife automatically gets 33% or 50% of his property as of the time he dies, even if he has a written will giving his wife nothing. But in this case, since the old man seems to be denying he is married to your aunt, it may be necessary for her to file a claim in probate court and prove she is his legal wife--that there was a valid marriage recorded in the state and there was no divorce. Even if your aunt wins that case, it doesn't necessarily mean she can get the house, because, as I wrote, he might have made a valid transfer of title some time ago. So the house would not be part of his estate when he dies.