Popping is pretty hard on an adult do to all that extra muscle control they develop down there. Your best bet for an accurate answer is that probe kit you plan on purchasing. The general size of the snake should be a relative indicator (assuming she was raised moderately well), but spur size and tail size can vary enough that you only be speculating by other visual physical characteristics.

Anyway, she's a good looking Pastel, congrats on the pickup = )