Well, there are quite some requirements to it.
It only ever works on thugs, guards, orcs and lizardmen (in v0.7). Then she has to fulfill all requirements needed for vaginal sex (meaning wet and sufficient desires and clothes) and the attacked enemy has to be erect (certain pleasure meter, indicated by blushed face).
And that only unlocks the potential for the kick counter. It actually happening depends on many different factors. As a general rule, you want the enemy to be stronger and either horny or angry (horny works better, except for orcs). Then some edicts can help, too. Guards are more successful if they have better training and stuff (i.e. aphrodisiacs, steroids, enhancements) in their food. Thugs are more successful if you chose stress relief in the thug crisis and weakening them lowers the success chance.
Note: all details can be found in the code, see spoiler below.
Now the thing that makes it difficult is that the scene requires vaginal sex to be possible. Meaning if enemies that can engage her in it by themselves (thugs, guards and lizards) and they act before she can kick, you'll end up that pose.
Thus, the two most reliable ways I've found are: focus on agility to make sure you go first or (and this is way easier) do it with orcs. Get an orc angry (massively increases success chance), keep other desires (esp. boobs) low enough to not end up in a different sex pose, raise pussy and cock desires, get wet and kick away. Two times are most often enough to get caught, if the clothes are loose enough.
And now... the
