I can't seem to find records of any other German, Austrian, or Holy Roman Empress being referred to by their husband's name. What was different about Victoria?
It was her own decision to be called 'Kaiserin Friedrich' (or 'Empress Frederick' in english).
She and her husband Frederick had very high hopes to change Prussia, and after 1871 Germany, into an English-style liberal constitutional monarchy once Frederick would become King of Prussia/German Emperor. To their distress Fredericks father, William I, almost reached his 91st birthday, at which point Frederick, then Frederick III, was already terminally ill, dying after just 99 days as emperor.
During the years of waiting not only grew the anti-liberal party stronger but the crown prince and his wife became more and more isolated at the court, they even came at odds with their son, later to become Emperor William II, which in return of course strengthened their bond with each other.
So, once Frederick was dead, Victoria ordered henceforth to be called 'Empress Frederick', to commemorate her late husband and the ideas he had stood for.