Despite the extremely unusual last/maiden name (I could find only one Ruth Wertheim in the US), and that the two women have similar birth dates, are from Germany, went through Westerbork, and survived the Holocaust, they are not the same people.
One of my next options is to contact Yad Vashem. I’m pretty sure the right way to look is to Israel, which is where the records say Ruth emigrated in the late 1940s.
As well, the family of the other woman is also being very helpful (after all, they share a somewhat unique last name with Heinz’s wife). I’ll be talking with them further and may find out more. It’s actually been quite a powerful experience to be able to hear some of this other family’s experience. Theirs is also a story of magnificent loss, survival, and triumph.
I just wanted to give an update. Things are rarely as simple or cut and dried as we would like, and certainly to locate someone 65 years later may not be easy. I will continue to look for Ruth and/or any of her relatives or descendants, or any relatives of Heinz.