In short, she was asked to guest edit a student literary magazine, and then the student editors disagreed with her editorial judgement. They didn't like the fact that she didn't effuse when she didn't think the pieces deserved to be effused over. They appear to have found her attitude of honesty to be at odds with their aim to make the magazine "an encouraging platform for new and developing student writers".
Those of us who want to be good writers, as good as we can possibly be, must be strong enough to allow (in fact welcome) professionals to judge our work. If we don't open ourselves to the notion that our work is not perfect, or is not even as good*** as it could be, then we don't deserve to improve. Or be published. Taking criticism is not easy, and I'm not saying we should always agree with it,. but we have to be open to it.
(*** corrected thanks to BuffyS's superior editing skills - but I'm not paying you BuffyS!!)
In primary school you might expect to be told you're doing brilliantly when you're not (though I question whether that's a good idea either ...) but by the time we're adults we have to face up to our short-comings.
Critique groups and writing groups are also often guilty of over-effusing and under-criticising; partly because when someone delivers negative crits, all hell breaks lose and the fall-out from deflated egos can be ugly to watch. So, if you can't take criticism in public, don't be published, because you'll sure as hell get it once you are. Instead, either find a trusted person and listen to that person's opinions or learn to edit your own work to within an inch of perfection. That inch is as close as any of us can expect to get, but we have to try.
If you remember only one bit of Diski's excellent piece, remember this:
"What surprised me most was how many of the stories felt unfinished, as if I were reading a early draft. Problems with structure, sentences that need to be worked on, far too many easy clichés not rejected - all of this normal for a first draft, even a second. For me writing is the editing. It's where the you make the story your own. Draft, redraft, let the thing sit, and then consider it again, read closely, carefully, cut away everything that you haven't properly thought through, and some things that you have."
It just about sums it up. Accept nothing less from yourself than intended perfection, even if perfection is rarely actually achievable.