Just a guess...

I'm guessing that the user is applying data|filter|autofilter, then hiding some
rows.

Then with the rows hidden, she uses Window|Freeze panes.

And then finally resets the filter (showing all???).

The cell that was active when she applied freeze panes is now off the bottom of
the screen--and everything above that cell is frozen.

Have her try using Window|Unfreeze panes.

If that works, remind her to only apply the window|freeze panes when all the
rows are visible.