Answer: When writers allow others to read their work, they open up an intimate part of themselves. So if anything bad is said about the writing, then it's like a kick to the gut. That's why writers have to develop a thick skin. Throughout any writer's career, no matter how successful you are (think about Stephen King's negative comments about Stephanie Meyer), there will ALWAYS be someone, anyone, there to make comments. They can range from high praise to down-right mean. If you take these comments personally, it will hold you back from doing what you feel you were meant to do.
Having said that, though, she couldn't have been much of a friend if she went around telling everyone how terrible a writer you were. Friends just don't do that. Friends support each other. There seems to be another problem between the two of you and it has nothing to do with your writing. (Don't want to be Dr. Phil here so I'll end it at that!)
To get passed the fear, you must develop the mentality that you will take constructive criticism for what it is; a learning tool. Then you must tell yourself that will recognize and not pay any attention to those whose comments are hateful, degrading, and over-all non-productive. And most importantly, you just need to keep working at your craft. Keep writing and keep submitting. The more you do it, the more you will learn, and the better you will be at it. If you want to accomplish your dreams, you just need to do it.
And it doesn't hurt to surround yourself with a support group. Look for online writing groups or local writing groups in your area.