This issue is very tender for me currently - my high school sweetheart (same era as you) came out to me as trans recently. Although her issues were different than this little girl, the lifetime of living with a body that has never matched her knowledge of who she is had taken (and continues to take) a heavy toll.
I am so grateful that she was willing to risk my reaction and share her life with me. The transformation in our relationship is nothing short of miraculous, and my delight in who she is (her description) has supported her dabbling her toes farther in the coming out stream - and she now, for the first time in her life, able to imagine that someday she may be able to live as herself. (I'm not claiming credit for her moving in this direction - but as the first outsider she told, a bad - or even hesitant - reaction would have been so discouraging.)
None of us should ever have to doubt that we will be able to live as ourselves - or be made to feel that our gender presentation is "wrong." Every time I hear a story like this one I rejoice in the hope it brings - and ache for my sweetheart who, as a child, was never allowed to hope.