She is a good point guard, no question. But a lot of her high assist numbers comes from Baylor's offense which gets players open for easy shots. Of course Johnson is a key part of running that offense.
She also gets a ton of assists from a pick and roll game that she plays with Davis. A lot of times Davis just fakes the pick and then beats her defender to the hoop. Johnson is very good at hitting her on her break to the hoop.