Maybe she thinks she's a horse!
They are notorious for this. My QH will trudge unbelievably slow when we're going away from home and tries to stop and eat all the time, but once we are on the way back, suddenly he's remembered that he can walk... and relatively fast at that!
I would continue doing short walks and you could try on the way back walking past the house instead of going right to it. I would avoid bribing her all the time, since you know she CAN walk on the leash, she just doesn't want to. I also think the obedience class will help you a lot as well.
Good luck w/ your girl!