Why do you think a heavier racket can cause injury? Probably the other way around.
The force of the incoming ball is a result of the weight of the ball (which is a constant) and the pace of the ball (and her opponents are going to hit faster balls).
The collision effect with the incoming ball is reduced with a heavier racket, and therefore less stress on hand, wrist, elbow, shoulder.
It is more the strings, string tension, gripsize and frame stiffness that are the equipment related risk factors.