That immortal godmother just really short-minded due she is too strong that her brain is like a kid who believe everything what people said (in this case Mu Siyun).
I feel pity for her secretary due her dumbness and craziness for Mu Siyun already beyond help. But, dont worry with her appearance, she can back to normal body in short time since angels rarely got chubby due they wasting so much energy for combat mode that they feel so hungry afterward.