But does the folder/drive that stores the file give her "write" permission?
It's much safer by the way, to only access via Open Remote... Should two users try to open the file directly, your file can be damaged.
It says she has write permissions but when she tries to modify a record it won't let her modify it. The external drive is only accessed by one person at a time or when via Open Remote.
I'd get a tech to look at your system. This sounds like a permissions issue with your computer and the fix depends on your Operating System and what options you've selected.
As a test, can she open the folder where this file is located and add a file to those listed or change a file name?