Ugh, what a rotten situation. It's especially crazy-making since you aren't really in a position of authority over this woman, and the people who are haven't been holding her accountable.
I'm so sorry. It sounds like you're doing great at maintaining your dignity though. I wish I had some good tips on how to get a sense of distance, so that she wouldn't be able to affect you emotionally though. You don't need the extra stress, and it just seems like an unfair burden to you.
Does it help to keep reminding yourself that it's just ... "x more days".. and keep counting down? I think your strategy of distancing yourself as much as possible is a very good one too!
I hope the time passes quickly for you. Maybe... this might sound goofy... but spend some time visualizing/imagining how you'll feel when she's gone? Like, really picture yourself walking into the office and knowing that she's not there, and she'll never be back there, and that you'll never have to talk to her, deal with her, email her, or clean up another one of her messes... ever again. Take a few breaths and imagine your life without her as *clearly* as you can, with as many details as you can, and try to soak up the feelings of relief? Then, remind yourself... that will all be real in... x days...

May the next few weeks fly by for you!!!