Not knowing her circumstances, and assuming she just doesn't want to pay for Childcare, I think that is VERY annoying, however, we dont know her circumstances, but regardless of circumstances, i think it is quite slack that she constantly chops and changes where the kids are every day, you'd think that you might ask friends/family etc. whether its possible for them to take care of the children on a more regular basis, whether its one day a week every week, or more.
Like a PP said, IMO they do need stability, especially seeing as (i assume) she works 5 days a week, and organises someone to take care of the kids, every day, not once a week for the week for something, thats very careless IMO.

But, i don't know her circumstances, maybe she can't afford Childcare, and doesnt have family who she can pay less than a child care?
but i think that someone needs to say "no i dont want to" for whatever reason, so she may start to see that she is burdening people by dumping their kids at the last minute (pre-arranged is a different story) by people who are probably doing it because they feel they have to, rather than want to.