I think Plan UK along with many of the international development organisations have been captured by the trans / queer politics.
Up until maybe around 10 years ago nobodoy in the media or writing publicity would have thought twice about refering to girls and sex discrimination.
But since the NUJ capitulated and the concept (ie political strategy) to imply that gender was the same as sex many people use without being aware they are basically giving in to a trend. (I am saying this as someone who unwittingly started doing it until a realised when trying to write something it didn't make sense.)
What might be more concerning in terms of supporting or donating to any organisation is do they actually state TWAW.
I think you might be surprised by how many development organisations do.
Is it Plan UK that has coopted IWD into a "March" where celebrities can have a selfie moment. I just cant remember.
And not being deliberately cynical but there is a crowded field of organisations promoting their work with "yong women". For instance there is Young Women's Trust who have had a number of reports that have cover very similar points to this new one. www.youngwomenstrust.org Sophie Walker is their new CEO