I always assumed that RE is short for regarding. I did not think it had any direct connections with Latin. When programmers were using RE, were they consciously borrowing from Latin tradition?
The example given is incorrect. RE in De re metallica means thing. De is the word that means about. Her example is literally About things metal.
The word regarding is from French:
RE- indicating a repetition, or sometimes used as an intensifier in French (this part of the word goes back to a Latin prefix, not the word for thing).
GARD- ultimately from Germanic WARDJAN to watch or guard or ward.
LOL! 
Not that my latin is great, but what bullsh*t these people come up with!! “De” means down/about,
“re” on the other hand is the ablative of “res” meaning a thing or matter.
“De re metallica” means “about the metal matter/thing”
edit: oops, too slow. sorry for the repetition!!
Haha.
I have to be ashamed of myself… 
That’s what I get for being such a gullible slacker. But at least my assumption is still right.
I sent her an email (I think it was a she) the other day. Keep your eyes peeled to see if she changes it.