I really don't know. I agree with what you say, yet it doesn't strike a chord with her at all. I don't know if its the fact that its a martial art instead of a "yoga" type class, or that the participants are involved in attack, or that because I'm sometimes over-enthusiastic and come home bruised up from breakfalls or have been roufhed up a little on shihonage, or because of the marks left by beginners trying to see if just squeezing a bit harder will make yonkyo hurt (and end up with finger marks all over my forearm (I don't mind it don't hurt that much) .
as I said I don't know. MA, are not for everyone I guess, and that's just her excuse. However I would really really like her to give it a shot, I'm sure once involved the gracefulness of the art will be apparent to her.
In any case , the women at my dojo are not large musclebound people either, she just finds the activity no in her taste for the reasons I quoted on this rather tricky subject.