You have paid for time. If she cuts your time short you should mention something about it.
If she is leaving bcuz you are a jerk and cuts your time short by a significant amount.. she owes you money back.
to only give you 30 mins when you have paid for an hour is wrong. Bad biz and others should know not to see her. I find it really odd that more than one person has done this to you.

If you book an hour and only want to stay 30mins and she doesnt' sell half hours... then you should leave the hour fee.