That actually sounds like a relatively simple one to resolve although the practicality might be a bit poor. The nonpolitical resolution is to use a space with 1 small unisex bathroom and insist that everyone keep it clean. If there isn't a consensus on who gets a special bathroom then there shouldn't be one.
So forcing everyone to change their meeting place to a venue with a unisex bathroom only is not political, but a trans woman using a woman’s bathroom is political?
Also, Helen still wants to be called Helen and still wants to be referred to as a she. By this logic, everyone must go by they/them? Or what?