Marina was born male, raised female by her mother to avoid becoming a dark priest and has lived as such ever since. I believe dialogue with one of the priests also reveals that.
I will try to avoid spoilers in so saying, but the boss you're referring to is not dysphoria, it's Dysmorphia, which is a reference to a different condition. Its name and imagery more than likely have everything to do with what the character more directly related to it is going through, instead--and you can fight it as any character, as far as I'm aware.
Not trying to dismiss the concept mentioned above, mind you, as I think Marina *at least* touches on some themes along those lines (if she is not outright intended to be a transfeminine person under this setting's dark-magic-fueled strangereal logic); the author is very thoughtful about the themes he explores, and such things are not done without intent, in my opinion.
Simply, I want to get the details straight on said boss fight, and to not wholely brush aside the character related to it... different though said character may be, I get the sensation there's more going on there than the story currently presents.