|Father:||Archibald Acheson (c1580-1634) (possible)|
|Spouse/Partner:||Hector MacLean, Lord of Dowart (c1570-1630)|
|Children:|| John MacLean (1604-1666)|
The history of Clan MacLean states that the father of Isabella was Sir Archibald Acheson of Gosford. However, it appears that Archibald's father Captain Patrick Acheson was born in 1558, making the connection difficult to believe. If Isabella had her son John in 1604, she must have been born prior to 1588. If that was the case, it would be hard to believe that her grandfather was less than 30 years older than her. One source states that Patrick Acheson of Gosford married Archibald's mother Martha Drummond in 1579. That would mean that Archibald should have been born around 1580, making it unlikely that a daughter Isabella could have been born before 1596 or so. If that were the case, John MacLean must have been born after 1612, and married at age 17 or younger, despite reliable sources that list his birth year as 1604. Furthermore, Peerage sources that list the children of Archiblad Acheson (including his daughters) do not list an Isabella.
In all likelihood, since both Isabella and Archibald appear to both have been born in the 1580s, and since Archibald, his brother, and his father Patrick (born around 1558) comprised the only contemporaneous Acheson family to settle in Gosford, Ireland, it seems likely that Isabella was Archibald's sister, rather than his daughter. Further support of this theory is the fact that in the Peerage sources, Patrick's daughters are not listed, whereas Archibald's daughters (all about a generation younger than Isabella) are. If Isabella was a daughter of Patrick, she would have been named after her paternal grandmother, Isabella Grey.