User cannot view or link work items in Boards that are unassigned to them

Question

Hi, I have a project with a basic process (Epic, Issue, Task). A user is trying to add a parent, an Epic, to a new Issue created through the Board view. In the drop-down menu for Work Items to Link, it only shows items that she is assigned to, none that are unassigned or assigned to others. She is also a Project Administrator and seems to have the same access/permission level as me but I am able to do that. What could possibly be the problem?