Stella knows many commands. And if I have a high value food in my hand she can be very quick and focused. Or if we are playing ball. Or if we are out for a walk and we are training. But for the run of the mill "sit" or whatever....a lot of times she either sits very s..l..o...w...l...y, or she just stands there. How do I get her to sit NOW when I say sit? Just would like her response to be snappier.