References for Isabel of Mar?

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Sir B.Burke: The Dormant and Extinct Peerage. London, 1866
Sir B.Burke: Burke's Peerage and Baronetage. London, 1999
W.K. v.Isenburg: Europäische Stammtafeln, Band II, Tafel 68. Marburg, 1953 (1965)
D.Schwennicke: Europäische Stammtafeln, Vol. II, Tafel 92. Marburg, 1984