Gone are the days when women have to worry about this. We are now to be thought of as equals, not as pretty accessories who have to look and act in a way that makes us demure and powerless. Besides, I can't think of anything more dainty than a little nugget of food.
You misunderstand slightly--but only slightly.
1--Yes, Japan is still an irritatingly chauvinistic society in a number of respects.
2--It's not really a matter of being decorative and pretty. Eating nigirizushi with your fingers is acceptable but perhaps not elegant. For an analogy, how about eating lamb chops or chicken drumsticks in a restaurant. You know how you're supposed to cut everything off the bone and eat it that way, but everyone knows it's tastier and more fun to just pick it up with your fingers and munch? Kind of the same deal. On the whole, I think Japanese women would prefer not to be perceived, in a fancy sushi place anyway, as eating coarsely; with men, it's kind of up to the guy and his sense of style.
3--With foreigners like you and me, sex is not entirely the issue: we do what we like, and it's a question of whether we give a good XXXX what the locals think. My opinion, based on 2 years living in Kyoto (plus a wife who speaks better Japanese than most Japanese people, is blonde and blue-eyed, and is a frighteningly clever cultural critic), is that if you're eating sushi in a fancy place in Japan (especially the Tokyo area), you need as a woman to decide what you want to say to others. You will be watched: there's no avoiding that. You can say, "I know how it's supposed to be done, so get off my case and put your eyes back in your head, creep" (eat with chopsticks). You can say, "I don't care what you think about anything I do or wear or whatever" (eat with fingers, dipping fish not rice). You can say something in between. But you can't say, "I'm just here to eat, so buzz off." That's not a real possibility. So it's a complicated trade-off. If you speak fluent Japanese, you have other (even more complicated) options, but unless you can get the average Japanese woman laughing (subtly but clearly) at her male accompaniment by out-talking him, it's not worth the fight: you just attract more tedious versions of the same attention, plus now they know they can man-splain at you. (To be clear: I don't
like this, I'm just reporting.)
4--If you dip the rice, the
chef will be sneering at you. It's up to you whether you care. (Me? I
hate the feeling that everyone in the place is thinking, "ha ha, dumb
gaijin, doesn't know his XXX from his elbow.")