I pretty much agree with the "leave it alone, there's probably more to it than you are aware of" camp here.
I would advise your friend to not "make it about herself".
And I mean it literally - if she inserts herself into this, it may generate the false impression that she "got him fired"fired booted" and stories like that can spread like wildfire both in space and time - they can follow you around forever, especially if no other public reason has been given.
Insert the appropriate version of "nature abhors a vacuum" for gossip.
In fact, consider the possibility of a probation + a last straw scenario and her situation is being used as cover. Don't feed into the narrative by inserting herself visibly and publicly.
I would also recommend against send(ing) the person who left a message unless there is a preexisting strong personal friendship - the motive could be totally misinterpreted, and emails can be forwarded forever...