Isabella's maiden name was minor. Information came from the family tree of President James Madison, that can be found here https://www.archives.com/genealogy/president-madison.html
Isabella's real parents were John Minor & Elizabeth Taylor. Her adoptive parents were Thomas Todd & Anne Gorsuch.
Isabella married John Madison II
https://www.wikitree.com/wiki/Minor-671 has disconnected her from any parents at all.
Please see the discussion below about her ancestry. No parents should be added to this profile without definitive sources.
20:10, 3 November 2017 (EDT) Lee-5956 for the US Presidents Project
Isabella Madison Was Not a known child of Captain Thomas Todd, I, of Toddsbury & Anna Oldton - their daughter was Averilla who married someone else.
Their point:
[Bob Allen, San Jose, CA - "MADISONS OF COLONIAL VIRGINIA (Revised)"] believes that Isabella Minor Todd’s maiden name was Minor, not Todd. First of all, middle names were not in general use in VA in the 17th Century, and were even more uncommon for women than men. Therefore, it seems unlikely that Isabella had a middle name. Second, President James Madison’s handwritten genealogy names his wife as “D. P. Todd.” It is well established that President James Madison married Dolly Payne, the daughter of John Payne and Mary Coles. Dolly Payne was previously married to John Todd before marrying James Madison, Jr. Yet when naming his wife in his chart he called her by her previous married name and only used an initial “P” for her maiden name. It would be consistent for him to have done the same with Isabella Minor Todd if she was a widow of Mr. Todd at the time of her marriage to John Madison, Jr.