I think that you basically just have to suck it up and stay professional. It is awkward because that is the nature of the business however, it doesn't have to be awkward for 4 weeks if you don't require such a long notice.
If it works for you, then keep it the same way but know that this will be the case most times.
There is no ONE right way so we gotta take the good with the bad. As far as the DCM saying bad things about you....well, let her. People who really know you, know it isn't true and if she wants to paint a picture of herself as a gossipy person, let her.
Be the professional and let it slide....put a star on your calendar and know there IS a light at the end of the tunnel, then they will be gone.
Have a nice big glass of wine at the end of the day and toast to their farewell!
