[Gerald]

If she's legit, then she's probably fed up with "no shows".
It's frustrating for all the ladies when a client books an appointment and just doesn't show up. In most cases it costs them money as they may have been able to book someone more serious. It's worse when business slows down and you have bills coming due.
In some cases, the lady may do a lot of prep work with hair, makeup and outfit only to be stuck waiting in front of the TV watching a rerun of Pawn Stars for 8th time.
Getting a prepayment is good insurance for all that.

However, it's not good business and I'd suggest avoiding anyone asking for a prepayment unless you are asking her to travel. Her risk of losing money increases with the time lost in traveling out of town so a small deposit becomes reasonable.
Risk and reward are what running any business is all about. If she wants guaranteed income, then work for someone who pays with a weekly paycheque.
Not only do you, as a client, risk a paper trail but you are taking a major risk in getting ripped off (as JeffD mentioned) and we all know how often guys get ripped off by providers. It's not like there is one bad apple in the bunch. Half the basket is rotten which is why this website has a review board!
You did the smart thing for multiple reasons.
Most likely she can get away with that in Sarnia, but she'd starve in London.