Mother has cll leukemia dr told her not to get a shingles shot (after the fact she already got one) what is the reasoning?

Attenuated virus. Your mother's immune system is somewhat suppressed due to her cll and perhaps her treatment. The shingles shot virus easily succumbs to normal immunity but when suppressed, it might get out of hand and actually launch an attack. If several weeks have passed and there is no problem, then there is nothing to worry about.