Note from moderator - I moved your post into the 'Mac Software' area of the forum for greater visibility.
In an ideal situation, swapping your D6000 dock with your friend's D6000 dock would help determine if the dock hardware is a contributor to the current behavior. However, given your distance apart it is understandable that is not possible.
Others have reported that upgrading the firmware of their D6000 docks can sometimes help with unexpected behavior.
However, the firmware updater from Dell only runs on Windows -->
https://www.dell.com/support/home/en...-d6000/drivers
Is there any chance your friend can get temporary access to a Windows system in order to ensure the firmware in her unit is up to date? That would help remove one more variable from the equation.