My border collies are the smartest, most obedient dogs.
My mother has a border collie, but I don't know much about them myself. Are they usually very obedient?
Yes, they are.  They typically dominate sheep dog trials and dog sports.  Is your mother's smart?
She seems pretty smart, actually. I've never seen a sheep dog trial, but I think it would be really interesting to watch!
oh they are great.  The dogs work sheep on a range of hilly unfenced land.  You should check it out.
Now I want to start working with my mother's border collie. Are they hard to train?
Not terribly hard.  Especially herding.  It's simply a modified predatory behavior that is already in them.