Hi Anne,
Thanks for reaching out. If a user is added as an admin, they can see and edit all properties created within a company. This is how the roles are broken down:

What permissions would this user need? The closest you can do to an admin is Approver+Publisher and then in the property option only check the box for the properties you want them to access.
Example (but with the role changed to Approver + Publisher):

More information here: https://marketing.adobe.com/resources/help/en_US/dtm/t_create_group.html
Best,
Tacia