I will make it clear from the outset of my comment that I am not talking about the child in the article - I have seen these types of threads go to swiss cheese.
For many of us, raised as girls, we can go through phases. Perhaps the idea of being dressed up like a doll (forced femininity) makes a girl reject this most strongly - I know I hated being dressed like a doll for weddings, when male cousins were not restricted in play by their clothing. Also what Transplants said, about being singled out for femininity treatment, in a sex-imbalanced family unit.
And the biggie, for many girls, the looming puberty ("what do you mean I am going to start bleeding down there?").
For some girls, it can be early realisation of being a lesbian. For others, even just the feminist awakening of "how come the boys can do that and I can't?"
And sadly for some, it is an attempt to escape being the victim of CSA. Particularly if the abuser says "how pretty" the victim is, you can bet your bippy the girl will do anything she can to make herself "look not pretty".
Many of us on this thread that we went through our stages, for however long, without 'gender intervention' by some clinic. Otherwise, if it were now, off to the GI Clinic we would go.
I disagree with all the photos being in that article. How horrible for the child later on.