For a start, her eldest daughter, Princess Victoria, would have inherited the throne in 1901. She was the dowager Empress of Germany at the time and died only seven months later. Her son Kaiser Wilhelm II would then have succeeded her and although his upbringing had made him less than enthusiastic about the British he might after a few years have got to like us better and prevented his two realms from going to war in 1914. He might even have changed his family name to, say, Hohenzollern-Saxe-Coburg-Gotha-Balmoral (he liked the Scottish castle: the photo shows him and his father Frederick III there, heavily be-kilted*, in 1862).
The Kaiser-King-Emperor lived on until 1941, and his son Frederick would then have reigned over the vast Anglo-German Empire until he died in 1951, to be succeeded by Princess Marie-Cécile (or Louis-Ferdinand? I've lost track). It is possible that all this would have been worse than keeping the Windsors, though of course not having two world wars wouldn't have been altogether a bad thing.
*mit der Schottenrock