Mary A probably has an account on numerous assets.
Quick & dirty check:
SELECT TOP 1000000
tblADusers.Username AS AD_Username,
tblADUsers.Userdomain,
tblUsersInGroup.Username AS InGroup_Username,
tblUsersInGroup.Groupname,
tblUsersInGroup.Domainname,
tblAssets.AssetUnique,
tblAssets.Domain,
tblAssets.Username AS Asset_Username,
tblAssets.Description
FROM
tblADusers
INNER JOIN tblUsersInGroup ON (tblUsersInGroup.Username = tblADusers.Username)
And (tblUsersInGroup.Domainname = tblADusers.Userdomain)
INNER JOIN tblAssets ON tblAssets.AssetID = tblUsersInGroup.AssetID
WHERE
tblUsersInGroup.Admingroup = 1
ORDER BY
tblADUsers.Userdomain,
tblADusers.Username,
tblAssets.AssetUnique
The tblUsersInGroup table contains account references for each asset.
What are you trying to produce? A description of the goal can only help.