I disagree with the advice given by Jason Anderson in Spot Reduction for Glutes. Doesn't putting a block under the heels for a squat destroy the knees?
Many thanks for your feedback and interest. If we take a look at an effective squat, it is an even distribution of forces throughout the ankle, knee and hips.
In this case, however, a female will often use the advantage at her hips and lean forward more, which places more emphasis onto her lower back and hips and therefore exaggerates the glute involvement and subsequent growth.
If I suggested the "sissy" squat, then I could understand your concerns. This may start to place a bit too much stress on the old patella tendon. However, all I am proposing is a more even distribution of these forces by allowing her to take some of that stress from her lower back and glutes.
Another consideration is that most people who step foot into a gym have poor lifestyle choices and positions. Therefore, they will have tight calves and subsequent reduced movement at the ankle and knee, which increases the stress placed onto the lower back. Again, facilitating a more upright position will help to correct this.
Summary: We cannot generalize and say that placing a wedge under the heels will damage the knees. What we can say is, the more upright we are in the squat, the more stress is placed onto the knees. However, this does not translate into damage unless taken to the extreme (i.e., the "sissy" squat) and performed repeatedly in an artificially stable and therefore identical environment like a machine, thus increasing the pattern overload potential.