Thanks. That's good information. Isabell Magruder is supposed to be the grand-daughter of Alexander Magruder the immigrant:
http://www.wikitree.com/wiki/Magruder-21
Her father is mentioned on numerous blogs and websites, none with any supporting documentation, but some with a lot of circumstantial evidence say she's the daughter of James Magruder, brother of Samuel Magruder and son of Alexander Magruder, the immigrant.
That website you gave me has a will of her husband and on that will is mentioned James Magruder, Samuel Magruder and many other prominent Magruders, so she definitely descends from this family, but, there's nothing that specifically states who her father is.