The trouble with photos of 'skinhead girls' from 1969/71 is how little they seem to have got into it - a bit of a hairstyle, maybe not even that, and clothing looking fairly mainstream. Not sure that this is subtlety, seems more like non-commitment to me. It is much easier to answer the question 'is she a skinhead girl' when looking at later photos.
You could be right but there may have been more to it than that, maybe they just did what they thought they could get away with in relation to parents and the wider society, it's not like there were many girls involved in the Teddy Boy or Mod eras. Seems like there were more involved in the skinhead times, even if they might not have looked so much the part.