definitely change coaches if she's telling you to use a forehand grip instead of a continental grip. On an interesting note, most of the top pros actually put a little bit of slice on their "flat" serves to give them better control of the shot. There was a study done (i think the results are somewhere on the boards) comparing ball spin of the serves of several top pros, and Sampras, the greatest server of all time, had a very large spin component on his first serve, which helped him get it in alot and thats why his serve was considered very "heavy". If you look at slow-mo videos of the top pros today like safin, federer, and roddick, you'll see that they swing left to right on the ball, putting slice on it.