Leaning back is generally more of a novice issue rather than a gender-specific one. It is training issue that would be corrected by an instructor. In the case of a female student, a female instructor might have been more comfortable, first to articulate the adjustments in different ways until the adjustment is achieved, or (with permission) make physical adjustments. Another interesting tool is the Coach's Eye app by TechSmith where the coach/trainer takes video of the student with smartphone or tablet, then can immediately play back and annotate to give the student a visual cue about where the correction should be. I haven't yet used Coach's Eye on the range, but have seen it used in other areas with success.
One gender-specific possibility has to do with footgear. If a woman is used to wearing heels, then leaning forward feels off-balance. (Lift up on your toes and try it! Also recall the feet of someone who wears heels all the time will get used to that position; and thus wearing flat shoes feels abnormal.) I've found that to compensate, knees should be bent and the hips tilted backward more than normal for the Iscoseles stance. "Bend your knees, stick your butt out and lean forward!"
Finally, another reason why shooters, especially older ones, lean back is due to vision changes. They are trying to get the proper sight picture. So modifications may need to be made; perhaps a prescription change, maybe change to a red dot instead of iron sights. Or, just grow longer arms!