Having never received one in my life (since I've never written anything I think is worth publishing... yet!) I'm a bit stuck on the format of afore said letter apart from the fact that it'd be along the lines of 'Thanks, but no thanks'. How would it be worded? Would they give her tips on improving her work for publishing?
Just a side note - This girl has a beta-reader rather then an editor, would this matter with getting published?
EDIT - Thank you so much for your replies people, I've now got her letter written and in the story, hurrah! Much love to you all ^^