Margaret Mowbray, m. before 16 Jun 1521, William Graham, 3rd Earl of Monteith

Can anyone expand upon Burke's here? CP gives Margaret Mowbray
married before 16 July 1521 William Graham, 3rd Earl (2nd line) of
Monteith, who died before June 1545 and had Margaret, b. 1527, wife of
Archibald Campbell, 4th Earl of Argyll (1508-1558). All that is said
about her family is that she was the daughter of a John. Is CP
missing any existing knowledge about her family?

Thanks,

Matt Ahlgren
.