Showing patience and repeating yourself versus showing frustration and putting your foot down?

I am not sure what the best way is to deal with my Mother-In-Law constantly asking the same thing.

Situation:
She goes in and finds her checkbook and asks about her taxes about every two weeks. And explaining to her that it has all been taken care of can be a bit challange at times.

My Response:
To be sympathetic to the fact that her memory is pretty much shot and to humor her and just accept that she will keep asking. I don't want to degraid her in any way as I know it's hard for her to give up control.

My Husbands Response:
He shows frustration that she is asking again and feels that he has to put his foot down and tells her that she has to stop and trust that he has taken care of it. He tells her that she is driving herself and him crazy because she brings the same thing up over and over again. He wants to hide the checkbook from her as he thinks it will stop her from doing this again.