I understand your frustration, as you pointed out many of us have to deal with this behavior. One question though...have you called her on this behavior? What is the point in having an "appointment" if you don't keep it?
You need to remind her...she agreed to the "appointments", if she truly doesn't feel well (or whatever) then SHE needs to reschedule for the next night and follow-through. What she's doing is losing your trust, I pointed this out to my H one time and it seemed to make a big impact on him....at least for a time.
If you don't bring this up...you are allowing her behavior to go unchecked and unaccounted for.
