Yes, as others here have mentioned, a lady's tour can end suddenly and unexpectedly due to personal emergencies and other surprises, even if you have called ahead the day before. I would be reluctant to book an entire trip based on one particular lady's availability. At Mona's and many other ranches, there are usually several other ladies on tour so as long as you have a bit more flexibility than "Mila or bust", you should be able to have a good time.