And how do we know that it was a lie? Did she admit it later? If she did, what were the reasons to believe her recantation over her accusation? Did the daughter say it was a lie later in life?

All I know from the article is that Wiener, a very smart person, thought the accusation was credible enough at the time to completely cut off people who were very important to him personally and intellectually. I also know that those people accused were very heavy drinkers.

It's safer to say we don't know anything about the veracity of the claim unless the reference offered some sort of material alibi.