Mark
Your not alone. The no call back has become a very disrespectful way of business. The Ad is probably just too lazy to commit to anything until the last minute. All you can do is be polite and request that she contact you with more lead time as you need to plan your calendar in advance. Confronting her or upper management never goes well, sorry to say your replaceable in their minds. Too many free "entertainers" knocking on those doors.
For the money they pay and the work involved booking and then doing the job I have little inclination to chase gigs in these places. Good Luck.