If most Aikidoka end up on the ground they have lost.
"ground fighting" is a complex technically rich discipline that requires serious study to become competent. That means cross training.
I am sure other folks here would agree that someone like Roy Dean or Micheal Fooks, Don MaGhee and some other would be good resources to find a good "dirtikido"
teacher in your area.
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.