I am gender non conforming, I am also very tall, I have a deep voice for a woman. I can count the times I got challenged in the toilets on one hand. When I respond, women realise I am female. No harm done. So don't worry about gender non conforming women, we will be fine.
Besides, transwomen in my experience are very gender conforming, they ooze feminine stereotypes: long hair, short skirts, make up, the lot. I think if I conformed to gender stereotypes expected of my sex, I would probably get challenged more, if that makes sense? So I never understood this line of reasoning by transactivists.