A few last things…These, I find odd:
Jewish or not Jewish. MMBQ seemed to think that the family was Catholic. Or am I mistaken? The whole religious question seems to be unclear. Why?
German speaking or not. Again, MMBQ says that she never heard Sylvia speak German but the brother says that she did speak German with her mother. Why was this concealed from her best friend? (Why would this even be unusual given that she was born in Germany?)
Last but not least…Why was Eva so convinced that MMQC knew where Sylvia was? Did she have a reason to believe that her daughter would want to leave/disappear? It doesn't make sense. The family was traditional and seemingly, quite strict. Why would a mother then be so willing to simply accept that the daughter left of her own accord under the potential cover of a good friend? (It sounds like the PI that was hired was asked to find her with the assumption that she was alive and had decided to leave.)
moo
ETA - IF the BF/F did go to SL's home to speak with her parents, I do believe that he told them something about the "argument"… Did he say that she told him she had had an abortion? Did he say that she told him the family was Jewish? Did he say that she told him she had a party while he was away? Whatever he told them, it was enough for them to think that they had to be discreet in her, and their own regard. It was perhaps enough for them to believe that he was legitimately telling them what had transpired and maybe, just maybe, it was enough for them to think that the repurcussions were such that she would want to leave.
BBM1: Unclear to us anyway ... maybe to them the word would be "private?" There is more on the Jewish/Catholic question earlier in thread 4, so I won't repeat that, but to take it a step further, it wasn't at all unusual, after the harrowing experiences of WWII, for some Jewish survivors to renounce their faith, to hide it, or even to convert to other religions. (Some WWII veterans, like my uncle, didn't talk about what they saw for decades either.) And it wasn't unusual for Jewish survivors to hide their backgrounds related to the war, whether out of fear of continued repercussions, or out of trauma, who can say.
Madeleine Albright is the perfect example. She was raised Catholic. Then, as an adult, when she was in public office, she was blindsided by learning that her parents were Jewish: "Albright was raised Catholic, but converted to Episcopalianism at the time of her marriage in 1959. She did not learn until adulthood that her parents were originally Jewish and that many of her Jewish relatives in Czechoslovakia had perished in the Holocaust, including three of her grandparents." It was all over the news when she learned about it. Most people's stories were not so public, but they abounded.
BBM2: This could be related to traumatic Holocaust experiences as well, or perhaps to Post-WWII contempt for all things German ... or it could just be "immigrant syndrome." (Doesn't actually exist, I'm being silly.) To assimilate, many immigrant families had rules about how they would deal with language. They might forbid the speaking of the native tongue altogether, restrict use to private times among family only, or even go in the other direction, speaking only English outside the home and only the mother tongue at home so the kids could maintain their language. Sometimes the kids were the ones who imposed the rules on their parents. I think immigrant parents tended to go along with these rules because they wanted their kids to assimilate and exceed them. My mother, for instance, denounced just about all things associated with her mother's Italian heritage, including language. Conceivably, SL could have told her mother not to talk to her in German in front of her friends. Because of my own experiences, I don't find it odd that ASWDH heard these conversations and that MMQC did not, but JMO.
BBM3: We have speculated about these things as well, but I do think it makes some emotional sense: It was the only thing that held any hope for her. Many other reasons are possible. Re the PI, we don't actually know what instructions the family gave, but it's possible. To my ear, from the little we know, it does not sound like EL ever suspected the BF/F or murder.
BBM4: If this is true, no one has shared it with us. JL, Jr., was present for this visit.