I was in pretty much the same situation as you, and criteria were almost exactly the same. Wife sat on a lot of bikes, and in the end, she liked the XR/CRF100 the best. Mianly because it was very easy for her to reach the ground, light weight, and not intimidating. We got her like new 2001 XR100 for $1,300. She mainly putts around where the little kids ride and she loves it.
She will likely outgrow it in a few months, but it will have served its purpose. That is, introducing her to dirt bike riding without scaring her. She can ride my KDX200, but she is pretty scared of it.
Buy a little bike, get her hooked, and then shop for what she really wants. Because in 6 months, what she really wants will be very different from what she likes now.
Another very good option is the TTR-125. That was Lori's second choice.
Scott