I tend to agree with Becky, American Blue lines can be weak. There is no safe way to prove her out to be a Platinum (100%). You'd have to inbreed the lines, further weakening them.

However, by breeding your male to a Pink Eyed Dilute(PEW) or Red Eyed Dilute (Example being a Fawn), you can see if he produces more "Platinums". That would be the safest way to find out. Obviously, you'd still be breeding your American Blue, but you wouldn't be inbreeding.