When an attacker is attempting to rape a women more than likely she will be on her back. It's a fact of reality. This is the most common situation for a women who is attacked. She will need to know some basic principles of wrist locks, arm locks or chokes to subdue her attacker. These locks and chokes can be applied while on the ground or on her back while standing. Perhaps this will force the attacker to stop the attack or allow the women to escape. The key here is subduing your attacker, restraining the aggression without brute force. The attacker could be 100lbs heavier, it want matter, because it's not about strength, kicks or punches, it's about restraining the attacker.
Newaza is important for an Aikidoka. We never can predict a situation no matter a persons skill level. Better to have knowledge of the situation, than not.
I highly suggest you attend some rape prevention courses. If a woman is being attacked (and Rape is about power) she needs to do everything she can to survive. Her attackers well being is the least of her worries.
A woman on her back and outweighed by a hundred pounds did not get there with her consent. She is more than likely already suffered some serious physical trauma and under some form of extreme emotional and/or physiological duress (and is perhaps already in shock.)There are specific simple guidelines to follow under such circumstances and perhaps the least of these is some type of choke or "wrist lock from the guard"...
Very few Dojos teach Rape Prevention the way it should be taught. Indeed 90% of the Rape Prevention Classes I see in Dojos are highly dubious. Your best bet is to invite a Local Law Enforcement Agency to come teach a class. Then perhaps you can exchange ideas about how to incorporate your "style" of practice into their training.
There is much much more to rape prevention than Waza my friend.
Back to the subject.