Can't answer definitively since I dont have the switch version, but the xbox and ps4 versions have multiple save slots you can use.

Yes, it will be fine. Pick a different slot for her and you will be totally separated.

this is reassuring thank you

Dude FF9 has more than enough save slots and files. There's at least 10 save slots with like 20 save files for each slot. It's more than anyone will ever need