Because I really don't think 'why do you believe you have the rights to notify a unsuspecting author about the PPC's existence and "PPCing" of this fanfiction' is a good thing to have said. It gives the impression of The Secretive PPC, Sneaking Around - along with The Fandom Police Will Stop You Talking To Each Other. It smacks of several gallons of elitism.
Guys. People are allowed to talk about us. 'Many members have agreed that what you just did is a Bad Idea'? This sounds like it's verging on a threat. I know it isn't, but - can you see how it sounds?
As to the topic at hand: there was discussion back in '05 or '06 about whether we actually ought to be telling
everyone we wrote missions of. The theory was that it would help them to improve. That died pretty quickly, mostly because several authors got very angry (I think there's a comment on the Wiki about authors trying to get missions taken down - yeah, that happened), but that doesn't mean we enacted a What Happens On The Board Stays On The Board rule or anything.
Regardless, I think the appropriate response here would be either to ignore it, or to post a friendly review outlining:
1/ Some of the points that you (probably Lily in this case) found needed improvement in the story - and also what you liked! Concrit is awesome.
2/ An explanation of who the PPC is - that we are a group of writers who use 'missions' to explore what needs improving in fanfics, as a combination of entertainment and learning to improve our own writing. I think that's a fairly accurate description, but if you think the key words I've avoided ('killing' and 'badfic', mostly) are needed, put 'em in.
3/ (Potentially, and if you have time and inclination) Offer to beta-read any changes or future chapters of the story.
I
wouldn't link to anything - wiki or mission. If she(?)'s that interested, she can hunt it down herself (and besides, I'm not sure FFN allows linking in reviews).
Oh, and take a backup of your mission in case it does get attacked.
hS
