(someone) thinks (someone) is the greatest thing since sliced bread

Translations
(кто-то) считает (кого-то) величайшим изобретением после нарезанного хлеба
She thinks her new boss is the greatest thing since sliced bread.
Она считает своего нового начальника величайшим изобретением после нарезанного хлеба.
Definitions
This phrase means that someone has a very high opinion of another person, believing them to be outstanding, impressive, or exceptionally good—comparable to how people once viewed the invention of pre-sliced bread as a major improvement.