I've just read the Amazon sample of I Am Jazz and I'm genuinely
and, to be blunt, increasingly angry.
Jazz explains the things they like - back flips, singing, dancing, drawing, mermaids etc and Jazz's best friends are girls and the implication seems to be that these are all 'girl' things - super 
But here's the interesting bit - Jazz also likes soccer.
Now. I'm a middle-aged Brit and, when I was young, football was very much a Male Thing (I'm glad to think that's changed quite a bit since then, of course, but I think it's fair to say it's still very male-dominated in the UK), but I've seen many accounts of American trans girls who are soccer fans, citing this as evidence that they are trans, which puzzled me.
On further reading, I've learnt that, in the US, soccer is predominantly seen as a 'girls' game. (UK football and US soccer are, of ccourse, exactly the same game - Association Football.)
In other words, football-mad UK girl = 'Ooh - could be trans'. Soccer-mad US boy = 'Ooh - could be trans'.
Or, of course, the adults around Jazz could have shown Jazz examples of male dancers, artists, soccer players and explained how silly gender-stereotypes are...