Girls should play in girls leagues for physical differences - I'm all for gender equality but since equality is more about having the same chances even though there are differences, I'm not for mixing up genders in sports, the differences are too big. What should change is the culture of rewarding, awarding, sponsoring, giving opportunities more to men instead of women.
When girls start to excel at traditionally 'boys' sports there should be a program that helps them nurture that talent. In the Netherlands you can have sports councilor at school/uni that helps you schedule school in combination with your sports education. The girl should have been given a chance like that, seems like her school was simply not able to provide a nurturing education on that level, so the solution should have been found elsewhere, she should have been given the chance to excel in a girls team.
No I know in some countries sports education is more tightly connected to 'school' - so I don't know if this would have worked for her. But a very talented musician would also go to a gifted piano teacher outside of school to nurture the talent, and so should this girls'.
That is one of the biggest hinge that push girls into bots teams. There are often situations where there is not a girls team that can foster the development of these elite female athletes. There needs to be programs in place for them.