I can't find a source for the death date 11 May 1644. I also doubt she was born or died in Wemyss. She's named Marie in the entry for her father in the Scots Peerage.
Born in 1563 - Islands, Orkney, Scotland Deceased 11 May 1644 - Scotland, aged 81 years old according to Stephen Duggan on Geneanet.
http://www.archive.org/stream/scotspeeragefoun06paul#page/574/mode/2up Balfour-Paul, Scots Peerage v.6 p.574]
Stephen Duggan, https://gw.geneanet.org/sduggan?lang=en&pz=shayla+nicole&nz=duggan&p=mary&n=stewart&oc=4
Stewart-216; Mary Stewart 1 Balfour-Paul, Scots Peerage v.4 p.286 Stewart-216 Mary Stewart 2 Stephen Duggan,
Stewart-216 Mary Stewart 3 [1]
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Name Mary Stewart Gender F (Female) Birth Date 14 nov. 1561 (14 Nov 1561) Birth Place Scotland, Scotland, United Kingdom Death Date 11 mai 1644 (11 May 1644) Death Place Scotland, Scotland, United Kingdom Father Robert Stewart Mother Janet Kennedy of Cassillis Spouse Patrick Grey; John Wemyss Child Lydia Ann Cooper; Anna Fraser; Jean Fraser; Simon Fraser; Thomas Fraser; Agnes Gray; Andrew Baron Gray; Elizabeth Gray; Elizabeth Gray; Helen Gray; Isabel Gray; Mary Gray; Patrick Gray; Andrew Grey; Jane Grey; Cecilia Wemyss; Janet Wemyss; John Wemyss