What the hell do i do?

So the first thing I need to let out is the fact that I cannot understand what I did wrong. Here is the situation, a girl was pissed that I didn't do something that she wanted, it was really small in fact, just something on facebook okay. Anyway, what I'm getting to is that when I try to make up for this, I get 'shat on' by her, she just gets angry and starts to spew her problems at me. About me, to me. WTF? What comes to me next is the fact that only one time have i made a mistake, ONE TIME, and a small mistake. So what happens next? Anyway, I don't really see said person as a long time hold, and to make it even better this person is not exactly 'friendly'. What really makes me hold onto this annoying occurrence is that this person has done so much worse, I mean so much. And I bet I really sound like a littly b***ch, but I can't help but feel like this is going to keep on happening. So again, what do I do about this?