Probably Most SP's are on the Pill. Most girls DO know roughly when their period start, whether or not the she is on the pill. ROUGHLY...within 2-5 days. Even on the Pill, the day of arrival can be a surprise.
Also, not all clientelle want F/S, so the fact that an SP is having her 'monthly' doesn't always matter. On that note, even if a client wants F/S, menstruation isn't always a deterrant.
So, if you made your appointment, she might not have known she would have her period in 3 days, also she might not have known you would want the full meal deal. Something else to consider is that she might not have felt well that day and didn't want to do F/S, so gave you the excuse that she was "ragging."
most of the time, an SP can still take appointments during her period because it is often easily hid, and clients would be none the worse for wear. Sometimes though, for us girls, we feel icky at that time, so we don't want to do F/S. That's when we'll let the client know.
Happy Pooning!!