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Hi Jean I have not received your email but have discovered this trail through Google and have joined the site so I can reply.
I do indeed have a copy of "Memoir's of the Camac's of Co. Down" which was edited by Frank Owen Fisher. It was commissioned by John Camac (1833-1896) of Philadelphia and La Roche, with whom Fisher seems to have been very close
 The book, was privately published in 1897 by Fisher in England, following its commissioners death. Despite its title, the book deals mostly with the Cammock family of Essex and Lincolnshire, only touching in the final chapters with the Irish family of the above John Camac which he claims to be descended from that those families.
The book does not I am afraid show Elizabeth Camac who married to Peter Reilly and I have no record of this marriage from Irish parish registers though I have seen it mentioned by Reilly researches in the Anglo Celt in 1998.
There is a later book, based on fishers research and published by William Masters Camac of Philadelphia "Memoirs of Camac's of County Down" Wm M Camac, 1913. This gives a good summary of what is in Fishers book and adds some later information on the American family and there intermarriage. It is available from the Family Search website but again does not mention your family.
Cavan is not a County associated with the Camac family in Ireland. Down, Antrim, Louth and Dublin are the areas they lived. The only connection that I can find with Cavan is a marriage between Eliza Marianmissa to Arthur Robert Newburgh of Ballyhaise, county Cavan in 1792. The Newburgh's children changed  there name to Camac Newburgh under the terms of the will of ELiza's father Jacob Camac's.
I hope this answers your query.