Why does Anna believes she is a freak?

Check out this quote from the book:

If Mr. Webster had decided to put the word freak in his dictionary, Anna Fitzgerald would be the best definition he could give. It’s more than just the way I look: refugee– skinny with absolutely no chest to speak of, hair the color of dirt, connect– the– dot freckles on my cheeks that, let me tell you, do not fade with lemon juice or sunscreen or even, sadly, sandpaper. No, God was obviously in some kind of mood on my birthday, because he added to this fabulous physical combination the bigger picture; the household into which I was born.

Anna felt she was unworthy to be alive, she had very low self-esteem.