This rider (Denise Serreti on Allure) has a fairly good elbow-to-bit line, but her hands are in a doggy-paw position. This causes her forearm to torque, which inhibits following the horse’s movement. It’s a minor complaint, but I’d like to see her reins a bit shorter and her arms a bit longer to keep that same contact.
To get her heel to come down more, I suggest she ride in a two-point seat. The balance of the two-point is the same as preparing to do a back dive— hips, knees and ankles bent to absorb the shock, and all the weight is on the balls of your feet. Your hands press on the horse’s neck, taking your full upper-body weight. If they don’t, your hips will tighten and your knees will grip the saddle to keep you upright, locking the shock absorbers. If her hips were properly absorbing the movement, at this point of the stride, her body should be bent forward, if anything. Two-point may help this, too, by encouraging the hips to bend. I’m not concerned about recommending two-point because her seat seems fairly deep already. When the two-point is easy (which I suspect it will be soon), she can do transitions to and from two-point, focusing on keeping the identical leg whenever she feels her heel creeping up.
In looking at this picture, I’d like to physically push forward between her shoulder blades and backward on her forehead. This would make the ear to shoulder-hip-heel line vertical, allowing her back to be stronger. This mare’s great attitude (as she indicated in her letter) is evident in her relaxed, enthusiastic, happy expression. Looks like fun!