I've known quite a few women like that. I will tell you first hand that grappling arts are great for women. I have been in Aikido for 15+ years. I can't tell you the number of tests I have participated in with women testing for their black belt....but have been "lit' up on several occasions.
That's another thing we don't do is hand out Black Belts to kids just because they have been there long enough. You have to be at least 16 years old before you are allowed to test for Black...because otherwise it just gives them a false sense of security. A 10 year old "Master" isn't going to over power an adult.
Joints are some delicate parts....and when you apply pressure to one....there will be a reaction. Maybe the first reaction ends the altercation....but if not...the reaction it generates from the person trying to ease the pain just exploits another avenue to take it in.
For example...a simple wrist lock can get a person moving in one direction to ease the pain....but now they have all their mass moving in that plane of motion. A simple reversal of that wrist lock now turns the joint the other way...and I can guarantee you that the other person will not typically be able to react to that unless they are trained.
That reversal with all the mass going in the opposite direction usually means something is going to give, and not in a good way. It's the premise of that art. You take their energy and intent and use it against them. And if their movement is too subtle...usually a tap to the ribs or face will give them the momentum you are looking for.
I've seen a 100lb woman accidently break a 200+lb guys wrist in class on accident because she followed through on the movement when she was supposed to let up during application training.
Now we also train most of the county police officers in our area. A good bit of them are smaller women. You should hear some of their stories about altercations with people resisting arrest just because they thought she would be weak!