It actually went much better than expected, if anyone reading this cares to know. Nothing got lost.
I first created her a brand new Apple ID with her own name and email address. I then went into Family Sharing on my computer and shared apps, iTunes and whatever else I could with her new ID, so she could keep what she already had installed on her devices, paid apps included, while using my ID.
Back on her computer I signed out of my Apple ID and then into hers, but as I was doing this I was asked if I wanted to save a copy of contacts, iCloud Drive, Keychain etc on her local machine. I said yes. Same story with her phone. Now any changes made to those above items going forward will not reflect in the others copy of it, but this is not a problem, because that's what we want to avoid. Now I can go into my contacts and she into hers and we can delete the ones we don't want any more, not that we cared about that, what we did care about though was sharing the same photo stream. I don't need to see the photos she takes of the shoes she buys and me of every beer I drink.
Either way, we still know each others passwords (I create them all anyway) so we still have unfettered access to each others devices, only now we have separate Apple IDs.
Moral of the story, while you can share an Apple ID with someone else, like we have been doing for years now, it's not really the best idea in the long, for many reasons, even if you trust each other like we do. So if you are thinking about doing it, rather not. If you get someone you know a new Apple device, regardless of who they are if if you live with them or not, but they don't yet have their own ID, get them their own ID too.
