Sounds like the pressure is affecting her.
Perhaps stand on the same side of the court and drop the ball right into the proper contact zone. Have her use a shortened back and forward swing and bunt the ball over the net from the service box.
Alternatively, set up a tennis "T-ball" and have her practice on that. It's a low pressure way to set up the ideal contact point and work on her mechanics. To improvise a tee, use a stool with an upside-down cup on top, with a ball on top of that.