Well, to back this up, Mary does say in her letter that she feels so ugly and pathetic. I can see why she would cover up a mirror.
Camera hack screenshots back this up. The covered mirror could symbolize this as well, with a double meaning perhaps.
Covered mirrors remind a mourner to look to others for sympathy and not to expect to be a tower of self-reliance and strength. Shiva is a time to look inward at the deepest parts that hurt, when superficial answers and the mirror’s reassurance “you look like you’re holding up well” do not help.
This is really cool...James definately was not a tower of strength at that point, and neither was Angela, who also had a mirror scene. The thing about Angela is though, she didn't expect any help from anyone, she couldn't trust people any longer, therefore I think the huge mirror in Blue Creek may have symbolized just how caught up in her own reflection (in terms of how lost she was) she was...And she was toying with a knife...
It's a little different with James though. I think when James was looking into that mirror in the beginning of the game, he was covering himself in his delusion. He was trying to "rely" on himself - to keep it together any way he knew how - instead of deal with what he had done. He was creating a false self, full of vanity (portraying himself as the strong and devoted mourning husband), not the deeply troubled man who murdered his wife in selfish desperation a day or two before.
Another stretched tie to this is his creation of Maria...In comparison to Mary, her vanity is way up there, or should I say James', since she is his creation, his delusion, to draw him away from the truth.
Anyway, excellent post adamblue, I really thought this was cool.