Hi Graham, can I ask what age is your student?, kingtrumpet offers good suggestions, in my experience most beginners have a tendency to over blow. If she is a youngster I would have her play very soft notes in the range to a second line G and have a competition with you to see who can play the softest, always let her win. Also check that she does not have excess tension in the lips. I have a friend that was taught by placing the trumpet on a book and playing open notes without touching the instrument, he claims to be a non pressure player but when playing above the stave his arms develop a tension tremor and his lips have a WHITE ring on them that takes several seconds to disappear, this is a sign of extreme pressure, the blood have been forced out of the lips. Regards, Stuart.