If it is of any help, we do 'full puberty' talks for girls at school at the beginning of Year 5, when pretty much every girl is 9. They used to be done at the age of 10, but we found that was too late for at least some girls every year. 'Basic changes' - hair growth etc - are introduced in talks in year 4, so age 8/9.
IME it is rare for the lessons we give to be a girl's first information about this, though we still do it because it is important for every child to know, and we don't want anyone to 'slip through the net' for any reason, including parental reluctance to tackle the subject.
DD knew about periods from a young age - perhaps 6, maybe earlier? Sanitary products etc have always been present in our bathroom, and she was naturally curious about what they were for. She had also seen that my body was different to hers, and wanted to know why and when hers would change.
I don't quite understand what her choice of plaything has to do with her need to know basic information about human biology that is already affecting her? Knowing about periods isn't going to 'contaminate' her, or make her 'less innocent', or cause her to 'grow up', any more than knowing about dinosaurs or ballet or cars or football or skating or space or ponies will. It's all information about the world.