score:4
The broad question has an easy answer:
Canon 901: A priest is free to apply the Mass for anyone, living or dead.
A search for requiem masses offered for the late Queen Elizabeth II will yield a large number, many of which were actually mandated to be offered in parishes by bishops. The Queen was a Protestant, and in fact died a Scottish Presbyterian.
There is no reason that they should not be prayed for by name in the Universal Prayer. We can't tell where they are or whether they will benefit from prayer, so we pray for them. Mass is offered for the same reason.
I am sure I recall reading that non-Catholics should not be included by name in the Prayer of Consecration itself ["Remember also, Lord, your servant(s) N. (and N.) who have gone before us with the sign of faith..."], but I can no longer find a reference for that. Others may know better.
Variation 1: It doesn't matter who asks for the Mass. It will be celebrated by a Catholic priest with his understanding of the sacrifice of the Mass.
Vairation 2: A lapsed Catholic is a Catholic.