Combat H is fairly limited. From what I understood:
1) Not all enemies will do combat rape attacks; the ones that do have a marker in combat, although sometimes this marker will not be displayed (at least for me; might have been a bug)
2) Each combat skill has a stat which is a percentage. This is the percentage chance for Elisha to be grabbed by the enemy.
3) If Elisha is grabbed by the enemy and your army has sufficient morale (the MP like resource which is used for skills), a soldier will automatically rescue her at the cost of a large chunk of morale
4) Otherwise, combat rape
I may be wrong on this though. I didn't find the demo of this game too interesting, so I haven't bothered with the full version.