Wow... I cannot even believe that is for real, that someone would actually write that response to you! I'm honestly shocked and appalled. It's disgusting!
Like others have said...
1) I can understand an author not having time or just not feeling obligated to read your stories and give you constructive criticism. But there is a tactful way to tell you that, and that obviously was far from it.
2) If you did somehow insinuate that your stories were better than hers, I can understand her taking offense to that... but again, there's a mature way to respond that doesn't include the flaming, personal insults, and rude language.
I can see Mare's point in encouraging you to reply to the author instead of starting a thread here, but personally, I'm glad you did, and I kinda wish I knew who you were talking about, cause that is someone whose stories I would want to avoid. Probably I already do avoid them, cause judging by the author's writing, they'd have too many grammar issues for my taste. (Lack of punctuation makes my eyes hemorrhage.)
If you're going to email her back, I would encourage you to keep it mature and "polite." Don't stoop to her level by calling her names or insulting her or her stories back. Reply once or not at all, and let it go. She's not worth getting upset over. If you enjoy writing, then keep writing, and forget what some deluded, raging egomaniac has to say about it. The more you write and read, the better you will get; it's as simple as that.