All I have is this;
If WWIV happened in, say, the 2050s and your story is in 2080, then most of the immediate radiation from the bomb would be gone.
Realistically:
Gamma radiation drops dramatically over time.
Most fallout isotopes decay.
A city hit decades ago isnโt automatically lethal forever.
Instead of the bomb itself causing her poisoning:
Prescott is bombed.
Nearby nuclear facilities melt down afterward.
Spent fuel storage is abandoned.
The Queen discovers an exposed reactor ruin.
This is more realistic than decades-old bomb fallout.