Hi johngirl,
Maybe you should explain to your sister about all the records being in the public eye anyway.
Anyone of your distant rellie's could follow
your line through, and put it on the Web, and it's best for someone in your family to do it and make sure that it is correct.
I followed the daughter of one of mine that had an illlegitimate son very young in the 1860's, more out of worry about what happened to her, to find her in later years married to a man with a very good job. I then found her son in later years, owning his own business.
I wonder what she means by your mum being a very private person, both my sister and mum were private people, but with regards to not talking much about their lives to others very much ...there was nothing to hide!
My sister died at 54, but I know this is the hobby she wanted to follow as we talked about it, and she had even brought some photographs up to me to try and sort out the background. Just as well because her husband destroyed everything after her death including all my parents documents.

... and I starting doing it on her behalf then.
Mum would have been thrilled about how I have traced her family back, and would have constantly needed up-dating on the progress. I think all three of us would have been addicted.
It must annoy your sister with what you have discovered, I bet she is envious of your skills really, and would dearly like to know what you know.
Ambers