Well, you could always get a nice bright pastel male to breed her to. Then the worst thing that happens if she doesn't prove to be a pastel is you've got a chance at making some nice light looking pastel babies that should have some really nice blushing and color! And if she does prove to be a pastel well then you'll have a chance at getting some supers! If you want to be really scientific about it though breeding her to a normal would be the best way to tell for sure if she is or is not a pastel.