If this cancelling behavior is something new that has happened with her lately, she may be under expreme stress from her mother, and like regular people, the 1/2 day may have been forgotten due to her mind being on her mom. But this is in no way to excuse her behavior, she should be a little more sorry for her last minute actions and try to get you into another appointment.
I know when my dad was dying, I wasn't the best of me at my job either. These things do happen, but she should make it up to you at least.