No the Bloody Mary thing is not true. And guess what - what you found isn't even the Bloody Mary thing! It's just a chain-mail attempt.
The Bloody Mary thing is a rite of passage for preteen girls. What you do is stand in front of a bathroom mirror (candle is optional) and chant her name a few times, and old Mary is supposed to show up. The story varies a lot. Sometimes you say her name three times and sometimes it's 13, and who Mary is and what she does when summoned can be just about anything. Some legends have her just showing up in the mirror and being scary, others say she'll attack and maybe kill you, and everything in between. But there's always a mirror and some chanting involved.
It looks like Mary has finally joined the online revolution, because now she wants to kill you if you don't send 15 emails. That's actually a small number to demand in exchange for your life, when you think about it, but hey... it's a recession and even mirror-witches are feeling the strain.
Anyway, both the mirror-witch and her chain letters are pure fiction. Would you like to know the real bloody mary thing? Little girls don't know the real version, so they made up the chanting stuff, but the real version is very real and it truly works.
What you do is mix up three pitchers of bloody mary, guzzle them all, then wait ten minutes and go into the bathroom. Guaranteed, you'll see all sorts of shocking stuff happen.