Employee refuses to do her coworker's work because her coworker is upset about her breakup 4 months ago: 'I was supportive, but now she's just milking it.'

She doesn't have to be cheerful every day, but she should be able to do her work. 

It can be really difficult to wake up every day and go to work when you're going through something extremely emotionally distressing. When I was going through a breakup of sorts, work was one of the only things that I felt I could consistently do. I was barely eating, sleeping, or hanging out with friends, but I knew that I had to go to work, and that structure kept me from sinking into a deeper, darker hole than I was already in. 

Showing up to work is only half the battle. It's much more difficult to pretend that everything is okay with your coworkers when you're emotionally spiraling. Nobody wants to be known as "the girl who cries at work," but sometimes you just can't help it! All that you can do is try to show up as emotionally regulated as you can, get your work done the best you can, and run and hide in the bathroom if you need to have a power cry. It's not glamorous, but it has to be done. If you're so emotionally distressed that you can't work at all, even if your company gives you the accommodation to work at home, then you need to look into taking a more formal leave of absence. It's not fair to you or your coworkers to show up to your job every day without the ability to get any work done.