I, and many others, have ridden horses in a rope-halters successfully. My horse is being ridden in a rope halter all the time, and we go perfectly fine in that. However, I am trying train her so that she can go well bittted, as well as bitless, in case I ever need to sell her. She knows how to give to pressure in a rope-halter, but when I change to a bit, she may give or she may not give, as it is different pressure and different cues.
If a horse doesn't know how to give and turn, then a horse doesn't know how to give and turn. Period. A bit won't magically make the horse know how to give to pressure, so don't think of it that way and try to use it as a "cheat." Unless she was already trained in a bit and goes well in a bit, you are going to have to re-train her either way - whether you use a rope-halter or a bit.