Losing one's marbles

It is a real pity to hear my mother ask the same question five or six times because she doesn't  remember my first answer.
- So your sister is going to a wedding today, she kept asking.
- No, mum, she's gone to a concert with her husband.
- I see. Who is singing in the concert?....
I  answered with the name of the singer and she would ask me.
- Then she's gone to a wedding??.
It is terrible...