The US Supreme Court case, Youngblood v. Arizona, 488 U.S. 51 (1988), controls in situations where "potentially-exculpatory" evidence is been destroyed. The case has been excoriated by legal scholars. The case will continue to control in Wisconsin.
Youngblood says that evidence can be suppressed from trial if a defendant is deprived of the ability to test it because it has been destroyed. However, in order for a court to suppress, the defendant must prove that the destroyed evidence was (1) "potentially-exculpatory" and, (2) destroyed in "bad faith".
Two problems: (1) It is nearly impossible to show that evidence was destroyed in "bad faith" (with "malice" or the actual intent to deprive the defendant of exculpatory evidence); and (2) it is nearly impossible to show that evidence is more than "potentially-exculpatory" after it has been destroyed. I'm sure no one knows that more than Ms. Weissinger.
The Supreme Court for Wisconsin has the authority to interpret the Wisconsin Constitution so that it provides more protection than the flawed Youngblood case allows. However, the court refused to do so in Luedtke and Weissinger. Instead, it stood behind that good old judicial maxim "stare decisis" (let the decision stand). Therefore, because these defendants could not prove the blood was more than "potentially-exculpatory" (because it was destroyed), and could not show "bad faith", the only test result that will go to the jury is the one the state lab produced. And there's your "due process under the a law."