Some brands will offer separate models for boys and girls. However, anthropometric data showed no notable differences between the measurements of boys' and girls' limbs.
Later in life, some women might choose to opt for female specific bikes, but at a young age this isn't deemed necessary by most experts, or most of the best kid's bike brands.
Liv bikes, the sister company of Giant bikes, is a women's only brand and therefore does cater just for girls, with options ranging from first balance bikes all the way up to 26" mountain bikes.
Most children will want a bike they find aesthetically suited to their own tastes, so most of the best kids' bikes will come in a range of paint jobs to suit the tastes of young riders.