Well it is done, I can't go and get the email back.
I had sent her an email reply and signed off as Lesley, and thanks to Google it mentions my full use Lesley Roberta.
She queried about the name.
And yesterday mom comments about my sister noticing the name spelling.
So I decided to just tell her the whole story.
Now I wait for a reaction, which I have no cue how it will go.
I hope it goes well of course.
I really have almost no contact with brother or sister in distant Ottawa, so it is not like she would be routinely exposed to my life.