Well, if you have a visual piebald male, then worse comes to worse you would have normal looking babies that are 100% het piebald. However, if you breed her to both your piebald and a pastel for a multiple sire clutch, you will then have no way of knowing which are the 100% het piebalds.

As for the markers, it is never certain that it means they are het piebald. I have a normal female that has the markers, but I already know she is nothing but a normal, not that it matters to me, I still think she is pretty.