Gothic BC

Ok, here's the jack on my work situation:

I work at a Chevron gas station five days a week, and two of those days I work graveyards, which means I am there from ten o'clock in the evening until six o'clock in the morning.  One of two people relieves me from these shifts, either the Assistant Manager, V., or a co-worker, A.  V. is always punctual (even early), but A. has problems with tardiness to the point of asking to be called to wake her up to make sure she gets to work on time.

Up until recently, I had no problem with that, but one morning before Christmas, despite my calls, she was over an hour late.  Two weeks later, she was also an hour late.  After the second instance, I told A. I would not be calling her because she is twenty years old and can wake herself up.

This morning, A. was 45 minutes late.  To make matters worse, I have to be back at work at two o'clock this afternoon, leaving me with a mere seven hours between leaving the store and having to return in which to sleep and go grocery shopping.

My query is this: How should I approach this problem with both my boss and A?  I, personally, want to punch A. in the mouth, but I think that will get me in trouble.  I have to see her this afternoon and I don't know if I can handle it.  I was shaking pretty badly this morning from trying to contain my anger and, to be honest, my sadness.  Any advice on how to tackle the situation diplomatically would be appreciated, because right now I just want to beat that skinny b*tch up til she cries...