I told her that if she wanted to e-mail a note to me, I would be happy to forward it to the staff for her. I did not tell her that she was excused from working or that she was relieved of the responsibility of finding someone to work her hours.
Days passed and she didn't respond. After five days I sent a follow-up email asking her to please let me know when she got the shift covered. No answer.
Halloween came and I went in for a few hours; she didn't show up or call to let us know she wouldn't be in. I was annoyed but there were enough other people working that there was no need to replace her. This didn't excuse her behavior, just negated the consequences.
So yesterday I had the pleasure of writing my first disciplinary letter. I tried to find a balance between friendliness and sternness, because several co-workers warned me that this employee tended to be emotional and liable to tears at the drop of a hat. I do feel a little sorry for her if she is too scared to ask for help from her coworkers, but if that's true than she really shouldn't be working in that position since we're a team that needs to work together and communicate with each other.