Is there proof that she went to Cambridge, or just the hearsay evidence from the friend who said she was traveling thorough Seattle on the way there to meet her husband?
It is not the hearsay from Susan Blake. I believe it is from a news report in a Chicago Paper. Although I have no recollection of what their source was. It originally came up when the Susan Blake interview was being dissected on the Long Thread--her recollection about the reason for the Seattle trip was wrong because he didn't go to Cambridge until August of 1962. A follow on to that was that she had in fact had her own trip there as well but it was in a later period. I haven't looked at that for some time--I don't really view it as a critical fact and haven't looked at the evidence.
That was in part responsive to the comment about abuse; but I suppose it would also be an important fact establishing the historical relationship--as has often been pointed out here, there is very little evidence about the relationship between Sr. and SADO.