the cane and ruler were administered to the buttocks in a bent over position either touching toes or placing hands on the knees or shins.
Well the cane seems to have done the trick in your sister’s case anyway. How old was she when she got that caning, and do you recall how many strokes she got? In her school (was it your school as well?), did girls get the cane over the skirt or over the knickers? If it was the latter, then I would think the extra embarrassment of having her knickers on display may well have played a significant part in persuading her that she didn’t want a repeat dose.
At the boys grammar school that I attended during the 60’s, I don’t think I ever heard of any boy getting caned more than once by the headmaster. Having occasionally seen the resulting marks in the changing rooms or the showers, I’m not surprised that they felt once was enough!