You can also tell, frankly, whether she drives a car well. Often distracted or on top of it?
Just as I wouldn't force a daughter into a microcar as a first car (what's safe about that?) I wouldn't by rote assume the smaller the better for a motorcycle. Women spend a lot of their lives being assailed by men as to their incompetence and this is yet another place not to do that.
I recall setting up camp in the Jackson Hole KOA on the way to Missoula 1984. It was raining and our group had come through major WY road construction where it seemed they'd taken the old road down to bedrock. It was a fun challenge to say the least on my R100RS. Another group of bikers at the campground contained a young woman who had her "maximum bitch" going. She was on some sort of KAW 250 chopper-look bike. Of course she was po'd--she was on probably the worst bike ever for going somewhere. On a comfortable BMW instead--maybe not so much I've always thought since.
Starting them out on crap is the wrong approach IMHO. Don't think "paying your dues" sells to their crowd.