I'd be interested in a source. I wonder how a giant mirror could persist in space without being shattered by debris and other elements hitting it from time to time.
This is a patent for stealth satellite technology. It's not a mirror, per-se, but it does demonstrate that there's interest in concealing satellites. Additionally, I'd expect that anything that could "shatter" a mirror would also be capable of shattering the entire satellite beyond operation; if we assume that statement is true, then the fact that so many satellites remain in service suggests that a mirror would also survive.
I think you have to leave your preconceptions about what a mirror is at the door when it comes to spaceflight. Much more likely to be something like aluminized mylar than a silvered glass mirror that could shatter.