I don't bother these days with half hour. I think it's probably the worst value for money and, if it's just one pop, then often you're done before the time is up. When I could come twice pretty easily in half hour, it was my most frequent punt length (besides walk ups). Too much like hard work these days so 45 mins a better option for that.
So to respond to the question: the extra time is whatever you want it to be, it's your money. My only advice would be to make her work for it. 15 min service for 30 min price is poor value.