Thank you for your very helpful, and quite cautionary, notes re Allens, Schoolcrafts and Montresors on this and the Schoolcraft forum. I have played with Hall's HISTORY OF EASTERN VT, somewhat with the VT State Papers vol. 6 of "Confiscations" etc., and have gained new "respect" for the life and depredations of Crean Brush. Incidentally, I am told that "Crean" is most likely NOT something Gaelic, but a surname used as a given name. An origin in Ireland might be do-able as I believe he mentioned a brother or brothers and a married sister. I suspect he is not Fanny's father, if Hall's abstract of his will holds true: 1/3 went to Crean's dau. (Mrs. Norman) by his first wife; 1/3 to the widow Margaret (and after her death, to Mrs. Norman apparently); and 1/3 to Fanny. One would think that, were Fanny his daughter by Margaret, that after M's death her portion would go to Fanny, her daughter. I'd like to see his will.
I don't have my notes immediately to hand but believe that Fanny's daughter Frances Margaret Allen may have given this name as her mother's maiden name when joining the order at Montreal. It might not hurt to check those documents rather than relying upon transcriptions?
Again, many thanks for your most insightful comments.