First, if that little sign is based on presentation, then should butch women and women in pants be going in there? The original intent of the pictogram was "women". I obviously believe that, through further science and learnings, we have expanded the definitions of both "men" and "women", but they are still the defining gate for those spaces.
Very interesting question, as I happen to consider them both friends, on and off this forum. So, I'm going to be obnoxiously direct about their situations by way of example here, because I know they'll understand when we talk about it.
IMO, Melissa looks more conventionally feminine (passable) than Suzanne does, ignoring her genitals. Suzanne has a vagina. If you saw both of them and didn't see their genitals (because they changed with a towel), then many women would be more accepting of Melissa. If they saw both their genitals, many women would be more accepting of Suzanne. So, in the end, I think they are both equally accepted on average, with differing experiences in individual situations. How comfortable THEY are in there is up to them. Nobody can rely on others to make themselves comfortable.
Also, to be clear, both of them are beautiful.
Personally, I agree that it's not enough to simply state your identity. I disagree that outward presentation is the next best thing, because we actually do have a way of legally recognizing gender identity, given certain reasonable criteria are met.
As I told Allie, I have no problems with our law in California that uses outward presentation, and would vote for it again, because in practical terms it doesn't cause a problem and solves a few, even if it does create some philosophically uncomfortable cases. That doesn't mean it's not worth exploring the philosophy.