How do I check this and if necessary, fix it?
The simplest thing to try at this point is select a folder on her Mac and get iThe simplest thing to try at this point is select a folder on her Mac and Get Info.
Look at the permissions section. Click the padlock and authenticate with her credentials. Her user name should be listed with me in parentheses. If it is listed, but no “(me),” select it and choose “Make ‘username (me)’ the owner” from the ellipsis pop up menu.
If there is a group (icon with two silhouettes), select it and click the – button.
If there is more than one “everyone,” select the one with two silhouettes and remove it.
Set the everyone with three silhouettes to “no access.”
If it says you have custom access, stop and ask for further directions. Otherwise,
From the ellipsis pop up menu, select “Apply to enclosed items…”
That should repair any permission problems.