I have no specific opinion on this. As I have no problem at all with Saints or extremely religious people having incorruptible bodies after death. Not do I think every claim to incorruptibility is necessarily genuine.
By all accounts this seems to be a genuine instance, so if you are nearby, maybe go see for yourself.
I also note that Sister Wilhelmina was ordained long before 1958, which means her ordination was made with valid rites, meaning she actually was a valid Catholic Nun and Abess.
Hat tip to JillyBear for bringing it to my attention.
