What do you call someone who doesn't observe details?
Obtuse or Thick apply in such contexts.
Caveat: Using these words for one's mom would be considered downright rude.
Obtuse
lacking sharpness or quickness of sensibility or intellect : INSENSITIVE, STUPID
He is too obtuse to take a hint.
Thick
obtuse, stupid
[Merriam-Webster]
Perhaps, you should go with imperceptive.