I don't believe it for a second...And of course it's impossible for any Catholic to prove such a thing...
More than likely there was some uncle or a family friend somewhere who was fervently praying directly to God thru Jesus just as the bible tells Christians to do...
Luke 4:27
"There were also many lepers in Israel in the time of the prophet Elisha, and none of them was cleansed except Naaman the Syrian.”
There were many lepers in Israel, but Elisha just healed one. And why? Because Almighty God knew, in His eternal wisdom, what kind of powerful and effective sign it would be: displaying His favor in just that particular case.
But why did Naaman ask for healing from Elisha? Why didn't Naaman go to God directly? Well, he evidently thought that Elisha was a powerful intercessor. And in fact, after Naaman's cure, he correctly saw it is a "sign" both that Elisha IS a prophet, and that there IS a true God in Israel: "THE" true God, since there is no other.
Did God not know that Benedicta McCarthy's parents and the rest of the family were engaged in intercessory prayers together with a powerful intercessor, Edith Stein (Sister Teresa Benedicta)? Did He not know that if He granted this miraculous healing, it would be seen as a "sign," both that Edith Stein (Sister Teresa) IS a saint in heaven, and that God hears and honors her intercessory prayers?
How is it that these miracles keep happening which confirm that a holy soul is indeed in heaven? Does God not know that His favor is invoked, in connection with an intercessor-saint?
God apparently goes ahead and provides the miracle, knowing --- intending-- that this will be a sign that, as He said in His Word, "The prayer of the righteous is powerful and effective" (James 5:16) -- even if that prayer comes from an intercessor who is already in heaven.