If you believe that royalty are somehow special and different to the rest of us . . .
If you believe that this special difference gives them the right to reign regardless of talent, ability or aptitude. . .
If you believe this right is transmitted through the bloodline to the nearest legitimate relative of the current monarch. . .

Then the current rightful King of Britain is an obscure Bavarian Prince - or possibly someone descended from an even early incumbent who got kicked out - and Mrs. Mounbatten has no right to a Jubilee of any kind because the magic wasn't transmitted to her as she is not descended from a nearest relative, but from George I, who was chosen not because he was nearest relative to the deposed James II, but because he was the person least like to cause problems for Parliament.