Doing the Washing - how does the mind work?

Mum's doing her washing today.  She lives in a high set house (a flight of stairs up to house, for those who don't use that Aussie terminology).  She has the ingenuity to work out its easier to put the dirty clothes into a plastic bag and throw them to the bottom of the stairs than it is to carry a basket down - being careful of her footing.  Then she mentions the machine overflowed last time (even though its just been fixed for that very problem - but that's another story).  She wonders whether it was because it didn't have enough clothes in it.  I try to reason this out with her, but cannot reach her reasoning on this obvious fault in the machine.  How can she figure out one problem but not another?  I can only conclude the brain works sometimes, and along some tracks.  Wish I could find out which tracks I can use too!